Not sure my STEAM library would fit on any phone, especially since most don't offer sd card slots anymore. I suppose if one could hook up a portable SSD drive. However I doubt it could also run my games at a reasonable FPS on my current monitor.
Realistically I would not mind using my phone for a casual PC. My biggest gripes about using a phone will never change. I don't want to use such a small display for browsing the web or playing games, and I have large fingers so typing and swiping just sux imho. Reading a book on a phone also sux, perhaps because I am older now and need 1.75 cheaters to even read my Kindle.