I really like what explainingcomputers did for their pi4 build, where they basically convert a m.2 SSD into a big usb thumb drive with a simple metal enclosure. Check it out, the timestamp you want is 6:25
I went this route as well. You can get a good quality usb 3.1 portable nvme enclosure for ~$20-$30 (be careful not to accidentally buy the msata version, which is cheaper but slower). Now you have a very fast thumbdrive! The main drawback is, unlike traditional thumbdrive, I can’t use it on my android phone. Not sure if higher end phone with usb 3.1 port can actually use it.
Your Android phone can mount an external drive enclosure over OTG, just make sure it’s compatible and formatted properly.
Depends on how much current the drive draws. If the m2 SSD needs more current than your regular thumb drive, your phone might not supply enough power and it stays unusable.
Besides that, as long a the enclosure uses the standard protocol and the filesystem is supported by Android, it should work