This (sightly overengineered) design allows you to mount (almost) any common smartphone on a vast variety of monitor frames. I use it primarily in conjunction with the android app Droidcam to use my smartphone as a webcam when I take part in an online meeting, but I'm sure it's also suitable for other applications.

The mount can be customized in several ways:

• With the upper countersink screw, the phone bracket can be adjusted from 100.5 mm to 180 mm in order to fit your mobile phone.
• You can also turn the entire bracket to adjust its yaw.
• Use the rear (thumb)screws to adjust the mount's pitch.

Required Hardware:

• Pitch joint: 2x 16-25 mm M3 counterbore screws + 2x M3 hex nuts (I also recommend these M3 thumbscrew adapters by Elothan)
• Yaw joint: 1x 16 mm countersink screw + 1x M3 hex nut (lock nut is best)
• Phone bracket: 2x 6 mm M2 counter bore screws (Optional - They just align the bracket parts)
• Some rubber or foam tape to add a little more friction to the mount's contact face

Printing:

• Solid filament (PETG worked well)
• 3+ perimeters
• 0.4 mm nozzle
• No supports (take care to keep the predefined orientation of the pitch clamp)
• ≤ 0.20 mm layer height