It is possible to hold a phone camera up to a microscope lens and take pictures. Holding the phone still is difficult and there have been many phone holder designs published. Those I have tried worked well but were too much bother to use. This design is simply a flat plate with a 29mm ring. The ring fits over the microscope eyepiece and the flat plate provides a surface to rest the phone on to help stabilize it. It works well for my purposes and prints up quickly.

I realized that the original file I created with Tinkercad had issues that needed to be resolved. Apologies to anyone who tried to print that one. The current v2 file slices and prints correctly.