I got very frustrated with other similar models I could find on the Internet, so I prefer to completely design it myself (using Onshape).
Just print it with 100% infill and normal support. It took me an hour at standard resolution using my A1 Mini and it's so good I decided to share it with you. PETG is highly recommended.
If you want it to fit exactly the size of your phone, tell me and I'll do it for you (free).
Real images including an iPhone 13 Pro MAX with perfect fit.
* New version with some improvement.