A parametric adaptor plate model, compatible with RAM Mount mounting hardware.
Refer https://www.rammount.com/

As presented, this adaptor integrates a RAM suction-cup base with an off-the-shelf phone cradle. See photos. You're free to tweak the design however you wish.

Note: When viewing the SCAD model, you need OpenSCAD version 2016.XX or better
Reasoning is because earlier versions don't fully support rotate-extrude(....) macro.