This mount will hold a Google Pixel 5 w Otterbox case. This means that this will not work with a bare phone (without a case).
There is no "standard" what I know for this connection. But I have used a few different suction cup car mobile holders that fit in either the four corner holes or in the center hole.
Example of one that fits in the center:
https://www.carldouglas.eu/en/products/mobile-phone/car-holder/581003
Picture example of holder models.
Check out my cellphone holders collection!
https://www.thingiverse.com/jeek/collections/cellphone-holders-collection
pixel_5_w_otterbox_on_general_plate.stl | 161.7KB |