The issue is that almost zero phones have custom roms available, and android is just a bad operating system to begin with. It’s designed much more around tracking rather than something like a server. You can’t do basic things like close programs or uninstall software or even choose how the memory is used. Basically unusable as a server for anything other than a toy. If you do find a ron for your phone somehow, it will suffer from many of the exact same issues. No closing apps, no access to the networking layers, massive security flaws due to a chaotic software landscape.