Disclaimer: I was a photography major in college (both traditional and digital studio process and editing besides shooting) and a working photojournalist for a minute when I was younger, still an optics nerd, from the user standpoint.
If you wanted a phone mounted lens for macro, I think the best system I’ve seen out there is the Moment cases and lenses. They’re supposed to be for photo enthusiasts who want to use their smartphone like an interchangeable lens camera, and seem to be much higher quality optics than most of the other stuff out there, but you’re getting into a $150 solution there, which is well within the range of getting a good USB/Bluetooth microscope, which will be more powerful but less versatile.
Lotta good reviews of that 100mm macro lens on B&H
https://www.bhphotovideo.com/c/product/1357296-REG/moment_120_002_new_macro_lens_no.html
I can’t find reviews other than some YouTube videos with sample images, which look good, but this is only $50. I tend to trust anything B&H sells even the cheap stuff is usually legit enough.
https://www.bhphotovideo.com/c/product/1768471-REG/apexel_apl_hb100m_premium_clip_100mm_macro.html
If your budget is around a hundred, you could go with a wireless microscope mounted on a gooseneck mic stand, which is what a lot of people here seem happy with, or get an inexpensive desktop setup like this one:
A random nerd note here: did you know that it’s not very difficult to convert an old digital SLR to an infrared camera? You just remove the anti-aliasing filter over the sensor and you’re left with a sensor extraordinarily sensitive to IR. It’s not quite the same as a dedicated IR camera but that’s a winter project of mine to do with an old Canon D60 and see what I learn looking through it at my grows and my leaky old house.
Edit: damn they even give lens specs, these are pretty legitimate numbers:
