That RFC does look like a nice improvement! Until then, since both devices have a ULA address, wouldn't simply deleting the printer from your phone/computer and re-adding it resolve the issue? Doing it when your public internet is down would probably even be best to ensure you're getting the ULA instead of GUA, thereby avoiding this issue entirely in the future.

(Admittedly I haven't had a printer for over a decade and I have never printed from a phone, so maybe I am missing something.)