The file 'Ender 3 (V2) Ball Joint Phone Holder 3D Printer Model' is (stl) file type, size is 462.5KB.
You only need a 25mm m3 screw/nut and a 10mm m3 screw/nut.
Now you can use your android phone as Octopi by using Octo4a app.
The ball diameter is 12mm.