After waiting for half a year on the Indiegogo, I gave up and built my own. The total cost is between $30 and $200 depending on what you have at home in terms of glue and tools.

A phone enlarger is used to make old-school paper prints of photos directly off of your phone. It works like a regular enlarger except instead of a negative you use your phone.

Materials:

$4.44 - 2x 2"x4"x96" wooden stud (e.g. home depot)
$2.45 - plywood. Often you can find cheaper off-cuts. (e.g. home depot)
$13.99 - black card stock (e.g. staples)
... 8x 1/4" washers
... 2x 1/4" nuts
... 4x 1/4" winged nuts
... 4x 1/4"-20 x 1 1/2 hex bolt
... 2x 1/4"-20 x 2" hex bolt
$no idea how much for the nuts and bolts but around $5?
$3 m42 adapter ring. doesn't matter to what it adapts

Total: $30

Adhesives:

$5.68 JB weld glue
$4.47 gorilla wood glue
$3.03 gorilla super glue
$10 hook and loop adhesive (velcro)
$15 Gorilla tape

Total: $38.18

Tools:

$3 protective goggles (yes, you need them this time)

The two biggest ones are (if you don't have them, they're a good investment anyway):

Drill (I got mine for $25)
Dremel rotary tool Mine is an ancient model so I can't tell you what to get. The only thing that's important is adjustable speed.

Some cheap bits and bobs:

1x bar clamp
straight edge ruler
pen
1/4" drill bit
Dremel multi-purpose cutting kit (it's magical!)
flush saw (optional, can use Dremel instead)

Disclaimers:

I live in the USA but I am european. You will find I am using metric measures for imperial sized materials - sorry about that.
Use the instructable as a rough guide, not as gospel. If you find that something doesn't work quite right, change it (and please let me know how you solved it :)

Step 1: Useful Tips.

Seriously, wait for the glue to dry before you continue.

Wait times:

5min Gorilla super glue
1-2h Gorilla wood glue
1h for drying, 6h to fully cure for JB Weld

Sometimes those wooden components will leave ugly gaps when you assemble them. You can fill gaps with a mixture of saw dust and wood glue. This will make the wood glue thicker and prevent it from simply flowing out of the gap you're trying to fill. So don't throw away your saw dust, you might need it later on.

Step 2: Cutting the Components.

This is where the Dremel multi-purpose cutting kit comes in very handy. If you've never used one before, make sure you first practice on a piece of wood you won't need. Always move the tool so that the bit is cutting in a clockwise direction. Otherwise it will wobble and you'll cut things you don't want to cut. You'll find out what I mean in your practice round ;)

You need:

1x Part #1
1x Part #2
2x Part #4
2x Part #5
2x Part #6
2x Part #7
4x Part #8

Yes, there is no part #3. Sorry about that :)

Parts #5, #7 and #8 are cut out of a 2"x4" stud and are used to build the frames for the top and bottom of the enlarger head. I used a flush saw to cut at 45 degrees so that the short edge is 16cm. This happens to be just big enough to fit my phone. There is no reason to make the frame square but I found this size to be easy to work with. Try to get your 45 degree cuts accurate, you want to eventually assemble them into a level square with equal sides and 90 degree angles which is harder than it sounds.

Parts #7 and #8 have a notch in them. The Dremel tool has an adjustment for depth - set it to 10mm for this cut. Make the notch wide enough for your plywood board to fit snugly. I aligned the notch slightly off-center. That way it will be easier to glue on the bellows on the bottom end and your phone will fit on the top end. Measure your phone to figure out how much space you need above the notch to make it fit and go from there.

I found those 4 notches to be the most difficult cuts in the entire project. Some tips:

15000rpm is a good speed for your Dremel.
Move your tool slowly, let it eat into the material instead of pushing the issue.
use 2x4 off-cuts as a guide for your Dremel tool. Clamp the piece you are cutting to your work bench.

Notice that part #7 has a circular dent on the outside. This will hold the bolt which will guide the head ends along the rail. Measure the head of your bolt 1/4"-20 1 1/2" (mine were 12mm diameter x 4mm height) and use the dremel #561 bit to carefully cut a cylindrical notch. It helps if you use your drill to start the hole. Some Dremel sanding attachments may also be helpful - use your own judgement. Start small and keep making it bigger until your bolt head fits flush.

Part #1 will eventually hold your lens. Use the Dremel bit #561 to cut a 18cm x 18cm square cut out of plywood. The size is the inner edge of the pieces that make up the frame (16cm) + the depth of the notch you cut into parts #7 and #8 (2x 1cm). If you decided to make parts #7 and #8 a different size, be sure to change the size of this part too.

The circular hole in the center of part #1 is where you will end up putting your m42 adapter ring. Measure your particular adapter ring to find out the correct size of the circle. I used an m42 to MD adapter so my diameter was 40mm give or take. Start with a smaller circle than you need. Keep trying on the adapter ring and increasing the circle size until the adapter fits nicely.

Part #6 are going to be the supports for your phone. The long edge should be the same size as the side of part #1 (18cm in my case). The width doesn't matter much, I went for 15mm.

Part #4 are the rails which are used to adjust the size of the enlarger head. Mine are 24cm x 2cm rectangles cut out of plywood with a 1cm wide cutout in the middle which starts 1cm off the top and bottom edge. The width of the cutout should be big enough for your hex bolts to fit loosely. I found the length (24cm) to bit a little longer than I need but it doesn't hurt anything.

Finally, Part #2 is going to be the lid of your enlarger head. I made mine from cardboard. I cut out black card stock to cover the front and back of the cardboard for a slightly nicer look. The reason I went for cardboard and not for plywood is that when I assembled my frames, it turned out they are far from level or square so using plywood would've left huge gaps which would leak light. Cardboard on the other hand is flexible and snuggles up to the skewed frame nicely.

Step 3: Making the Bellows.

Fold a bellows that fits the inside edge of your enlarger head. I cut out each wall of the bellows to be 16cm wide and I used the full height of the card stock but it turned out to be a bit more than I need.

I followed this great instructable for folding the bellows. Some changes I made:

I used card stock from Staples instead of bristle / bristol board (whatever that is :).
I used black gorilla tape instead of hokey stick tape just because I had some handy.

Step 4: Building the Scaffold.

Now that you have all parts cut out, you can build some components.

Use 2x part #7 and 2x part #8 (see step 1 for description of the part numbers) to build the bottom frame of the enlarger head. After you've glued together 3 sides, slide part #1 into the notches and glue on the 4th side. I used wood glue and found that I didn't need any nails. Give the glue plenty of time to dry and make sure you're building right angles before it dries out. Make sure that the two part #7s are on opposing sides.

Use 2x part #5 and 2x part #8 to build the top end of the head. This top end will end up holding your phone. Make sure that parts #5 are on opposing sides and that your angles are 90 degrees. The phone supports (parts #6) can be fit after the fact so you can leave them aside for now.

Step 5: Attaching the Bolts.

The size of the head can be adjusted with a nut and bolt construction.

Use a small amount of JB Weld to line the circular hole in part #7. Insert the bolt and squish a washer onto the excess JB weld that comes out when you press the bolt against the frame. Make sure the bolt is upright and not at an angle before you let it dry.

Repeat this procedure 4 times - 2 times on the bottom end and 2 times at the top end of the enlarger head.

When it is all dried out, you can assemble the rails and wing nuts. I found that I need to use 3 washers total (2 inside, 1 outside) because the threaded bit of the bolt was too short otherwise. If you have different bolts, you may get away with fewer washers.

Step 6: Attaching the Lens Holder and Bellows.

Attaching the lens holder is fairly easy: insert it and fill the gap between the edge of the hole and the adapter ring with JB weld. JB weld is fairly thick but it will flow until it dries. You may want to make sure that things don't move out of shape while drying by resting the piece with the adapter ring pointing upwards.

After the JB weld is dry, you can attach the bellows. There are a few ways you can go about this. I used gorilla tape on the bottom end and wood glue on the top end of the head. I also used a few staples to keep stubborn bits down. If you are better with your hands than me, you may get away with just wood glue.

Step 7: Attaching the Lid.

I decided that velcro is a good way to attach the lid to the head in a way that will keep light inside.

Use gorilla super glue to attach the velcro to the wooden frame and to the lid. Velcro adhesive is pretty strong so make sure you glue it on well. One weakness of this design is that if you press the Velcro too hard, it will be stronger than the cardboard lid and the lid may get damaged when removing it.

Step 8: The Neck.

I won't go into too many details with the neck because I found it's not a very good solution - the head with the attached lens is a bit too heavy. I was not able to use winged nuts for adjusting because they can't be tightened enough for the neck to stay in shape. I had to use hex nuts and use a wrench whenever I want to adjust the height of the head.

I used this instructable for inspiration.

Let me know if you find a better solution for the neck.

Introduction: Darkroom Enlarger for Phone