I designed this two part phone holder as exactly credit card size. Only a little bit thicker (2mm). You could carry in your wallet all time.
Just you need to print it
If parts are too tight (cause of printing quality) you can use correct file for your printer tolerance.
Easy to use also helps in cable organization.
If you don't have 3d printer, you can cut any 2mm plate (acrylic, plywood, ect.) with laser cutting machine or cnc milling machine.
...or, If you have precision hand you can take ordinary print of this .pdf file and cut the plate with fret saw.