I designed this specific model, but took heavy inspiration from @MaOI on Printables. No parts are directly shared between the two, and no design files used, but it served as a base for my design, many thanks to them.

Link to @MaOI's model:

https://www.printables.com/model/230901-mobile-phone-telescope-adapter

I tried a few different phone mounts for my telescope (Apertura AD8 dobsonian), and couldn't get any of them to work well with my setup. The best one I found was by @MaOl, massive thanks to them. Their mount was really good, with great concepts, but didn't work for me. The rail that the eyepiece clamp mounted too was way too long to fit my scope, and the M5 hardware I used wasn't really compatible. The eyepiece clamp was also much too big for standard 1.25" eyepieces.

I didn't have any design files, and there were a lot of minor tweaks I wanted, so I remade it completely to fit my hardware, using no original files. I removed the internal barrier on the phone rail, so if your camera was far to one side, the eyepiece didn't have to sit super far over. The new nut holes are ~8mm wide, and 4mm deep, should fit almost all M5 nuts, and I flipped a few of them (the rail for the clamps also fits the nuts and holds them). I also made the clamps bigger to fit bigger phones with thick cases, like mine, and a few other tweaks for stability.

Hope this works well for someone.

Print everything with supports, print 2x clamps. I will add a clamp STL for 2" eyepieces soon, currently this fits 1.25" eyepieces.

You will need:

2x M5x12 bolts

2x M5x20 bolts

4x M5 nuts

Reference photos for assembly.