This is a remix of http://www.thingiverse.com/thing:309809. I did not like a few things in this design so I revamped it a bit. First I wanted to mount the phone in the middle of the handlebars not at one side. So I sliced up the original design so I could get the mounting bit rotated 90 degrees. I also extended it so it would sit a bit higher up given the new location.
The original was one part which seems nice on the surface but creates a print that uses a lot of plastic in supports. Thus this is in two parts. I chose to use a threaded insert rather than nuts to hold it together, nuts can fall off, these inserts cannot. The inserts are found here (http://www.mcmaster.com/#99362a600/=s9e8hv) and I used a standard 10-32 flat head screw for the rest.
I also rounded most of the sharp edges, something I do on almost anything you might handle.
Print both parts
Thread in the inserts. I used a long 10-32 screw and two nuts jammed on the shaft as an insertion tool. After the insert is flush loosen the nuts and take the screw "tool" out. Works great.