Someone bought me a universal digiscope adapter and I previously tried to to make one with a cheap phone case and plastic cup. Both however needed me to remove my phone case which is not easy or desirable. I have a pair of binoculars, a microscope and a scope I want to fit my phone to. I decided the easiest option was to make my own using a 3D printer, using OpenSCAD to enable easy customisation, make a different adapter for each device, as adjustability can introduce weakness . The tricky bit was working out the camera position accurately, seems to work fine apart from at maximum zoom when the exit pupil gets very small and I slight vignetting. I even included recesses for the phone buttons. To make different ones I need the length and diameter of the eyepiece and the focal plane distance. I made it slightly oversize to enable me to get a snug fit by adding a bit of gorilla/duct tape. Nice and snug and robust. I ran them off on a polymer extrusion machine, but you could get them laser sintered if you wanted.
PeterW
PeterW