This is a very minimal design for a smart phone stand that can be downloaded and 3D printed easily. It also functions as a keychain so you never have to forget to carry it around.
Just input your phones thickness around the edges. If you have a phone case, input the phone thickness with the case.
The rest of the parameters can be played around with to complement your phones size and weight distribution
The smaller it is, the less stable it becomes. So you sacrifice portability for stability.