I can personally recommend
https://www.amazon.com/Awarded-2018-Best-Compound-Microscope/dp/B0094JTZOU
as it's what I use, with
to record videos on your phone.
I snagged mine off ebay for $100 from a bio student, so deals are out there.
I got a mileage out of this one before going dedicated camera
In order of difference importance:
If you're getting a trinocular scope and want to use it with a cell phone, you must either get an adapter with an included lens or pop an additional eyepiece onto the trinocular tube. I suspect you might get better image quality with a standard eyepiece but I haven't tested that.