>Phone cameras can't come close to the quality of even a full frame DSLR, anything medium or large format is light years ahead of phone quality.

This is true for medium format if you're doing a drum scan of the medium format negative. Realistically, however, most medium format negatives are never going to be drum scanned.

If you're scanning with a flatbed or via a DLSR, then the difference in quality vs. a modern cell phone camera is not huge. With a typical flatbed you'll get less resolution than a modern cell phone camera; if you scan with a DSLR and macro lens you'll get a bit more (but it's laborious, especially for color negatives).

It's possibly a bit counterintuitive just how bad a job flatbed scanners do in the case of medium format negatives. Years ago I was very excited to make my first scans of some 6x6 negatives with a consumer Epson flatbed scanner. The resulting photos showed about the same amount of detail as roughly equivalent photos taken using my iPhone 4S. There was far more detail on the negatives, as I easily confirmed with a loupe. Extracting that detail via practical scanning methods is far from trivial.

The other point to consider is exposure, color and dynamic range. Modern phones do a fantastic job here.