Universal Phone Tripod Mount. Should work for screen sizes from 4" to 6". It is designed to inprint M6 nut. At the end of layer 23 you have to insert the nut (with 0.3 layer height). Second thing you need is a rubber band.
Things you need:
Any rubber band
This thing is made in onshape, and it's fully customizable.
Onshape Link: https://goo.gl/0UkBNm
I was attempting to make this thing fully 3D printable, but I failed at making the spring because of plastic properties.
Put supports just under the rubber band hook. Nowhere else !
Bit of sanding
The rails/bars on the top part, that slides into the bottom part might need some sanding to move smoothly.