iPhone 14 Pro Loupe mount
A slip on mount for iPhone to hold a loupe. You'll want to modify this to adapt for your focal distance and loupe diameter, but this should be a helpful start. The adaptor slips on the top of the iPhone 14 Pro (with case on) and centers over the bottom left lens (Main Camera).
For my use I took a CCD lens out of an old scanner - these things scale 8.5" pages down to the 35mm CCD width, but more importantly these lenses are super low distortion.