Phone Mount SR

Parts:
1x M6 x 85mm
2x M3 x 10-15mm
nuts for them
spring - I used a brush spring for a 7.8mm diameter motor

Gopro knob:
https://www.thingiverse.com/thing:163883

The handle should be suitable for phones with a width of 68-95mm and a thickness of up to 13.5mm. You can attach a little smaller giving thicker rubber washers in the fixing points.

All elements except "base.stl" do not need support.
Base.stl (when your printer has a problem with bridges) can be printed with support, when setting the angle of overhang to 85.