The pattern is achieved using infill. In your slicer, set top and bottom layer counts to 0. I suggest using the honeycomb or gyroid infill. Silk PLA is suggested. Very minimal material is used - perfect for using up the remaining bit of filament

3 gap sizes available if you are using a phone case or thicker device: 10mm, 12mm, 15mm. These are slicer-scalable too.

The hole in the base is designed for use with a carabiner or similar.