I have a Chromebook with an ~11 inch screen. It’s basically the minimum size where a keyboard is still useable. I like it a lot, but it’s actually too big when I want to use it as a tablet.
I think this is the tension. Or maybe we just need to master one handed keyboards.
At least some of the time, when people refer to using their phone as a computer, I think they're talking about plugging into an external monitor through USB-C, and using the phone as a desktop with a keyboard and mouse.
I've tried every so often, and while I think all the hardware is there, the software wasn't. Perhaps Android has improved on this recently? I know there have been niche attempts in the past, like Samsung DeX or Ubuntu Touch, which may have been more solid. I've never tried out any of those.