Phones dominate not because of screen size but because the operating systems they run are fundamentally more user friendly. iOS/Android were the first time experienced OS engineers were able to go back to the drawing board and rethink the whole stack from scratch. They learned a lot of lessons from what worked and what didn't on generalized desktop computers and were able to build something people prefer using.

That's a rare opportunity. I hope someone gets a chance to do it for professional workstation computing one day. The Windows codebase has IMHO reached end-of-life. The Linux community isn't going to stray far outside the bounds of the 1970s era UNIX design. Apple does OK but they can't/won't change the macOS UI in any meaningful way and not enough people write native Mac apps to justify trying to do anything interesting there. ChromeOS is basically just a large screen smartphone OS experience with some Linux virtualization on the side. We're caught in a local minima.