A remix of: http://www.thingiverse.com/thing:614516
I liked the easy print simple design of this, but didn't like how the bottom part was so close to the iPhone button so I redesigned it to have 2 bottom parts and 1 top part.
It doesn't make the print that much slower to print, just 3 parts instead of 2.
I also moved the center down a bit so that the top part can flex and snap the phone into place a bit better.
This version is sized to fit snuggly on my iPhone 6 case: http://www.thingiverse.com/thing:481870, but it would be easy to modify to any phone dimensions.
An exercise I am thinking about is to make a customizable version so the length, width and phone/case thickness could be entered.