Here's a simple and elegant bike phone holder which can be made to fit almost any type of smartphone out there. Yes, there is already a large number of phone holders on the market today, but majority of them are either phone-specific, too large, too expensive or just don't look so nice on your bike. The holder described here is easy to make yet sturdy enough for hard road cycling. At least it's been serving me well for the past year or so.

Step 1: Parts

Things you will need:

Hard plastic phone case. These are readily available at your local phone shop or eBay for as low as few €/$/£.
Rubber band. The band should be tough, so don't use an ordinary household elastic band. A hair rubber band, for example, should be fine.
Patch of rubber. An old inner tire is a good source.
Glue or double sided adhesive tape.

Step 2: Cutouts

Using a drill, dremel or plasma cutter, cut out 2 hooks as shown in the image. Note the shape of the hooks, you should make them narrow at the base, so that the rubber band can snap-in.

Step 3: Rubber Interface

Using glue or double sided adhesive tape, attach two small pieces of rubber or similar material to the back side of the case. This will prevent the case from sliding around and will also absorb a part of the road shock. Depending on the position of the holder, you might want to stack a couple of rubber layers to "shape" the interface between the case and the handlebar/stem. I'll be mounting mine on the stem, so two single patches will be sufficient here.