This is my first model that I've designed and uploaded to thingiverse, so be kind.

Made this holder for my Oneplus 6T that also have case around it.

Maximum size the holder can support in a nice way is a 12 mm thick phone/object until it reaches the slip protection edge. The print holds the phone in a 55 degree angel.

The "back" have a smaller surface than a regular phone because there's no need to have it covering the whole backside of a phone. If I'm wrong, feel free to make a remix of it.

I have a Duplicator i3 Plus

I printed with;
0.2 resolution
PLA
20% Infill