so, Linux does work, a lot of stuff works. There is nothing fundamentally different about phones other than them basically all running on ARM instead of x86, which is more common for PCs. More development of stuff for X86 Linux than ARM Linux, although less of a difference than there use to be.

Really the issue is proprietary stuff built on top of android and IOS. Stuff that a lot of useful apps rely on for security and functionality. For instance banking apps are super locked down for obvious reasons, but the standards that have been adopted by the industry for mobile banking are all entangled with proprietary close source stuff.