After printing http://www.thingiverse.com/thing:78071 and finding it a little too big for my microscope, and a little too complex/unsecure, I decided to make my own for a 30mm tube/eyepiece, with much fewer parts.

The main part is a clamp that goes around a 30mm tube/eyepiece, with a section for vertical adjustment. It clamps down with a pair of M3x12mm screws and nuts. If other diameter clamps are requested, I can make those as well.

The other two parts are what holds the phone, they're simple clamps, the main part has the horizontal adjustment, and attaches to the main clamp with a pair of M3x6mm screws and nuts. The other part of the clamp attaches to this part with 2 M3x30mm screws, which thread directly into the 3D printed part.