Get a cheap $1 laser pointer from the dollar store or online store such as LAZERER and disassemble it. It'll look something like this when its disassembled:
Step 2: Extract the Lens
In between the first and third segment there should be a lens that focuses the laser. This can be in different place depending on your model but you'll know it when you see it. Eventually you'll find a lens that looks like the one below.
Step 3: Attach the Lens to Your iPhone
Attach it to your iPhone using a small piece of tape stuck around its edge. It should be small enough that it doesn't interfere with the view of the iPhone.
Step 4: Ready to Take the Marco Shot.
Take amazing macro shots! Note that the depth of field is extremely narrow and you'll have to be less than an inch away from your subject. Though you can get some pretty amazing shots like below.