This makes a lot of sense for tablets - but Apple decided they won't allow it in order not to cannibalize sales. For phones, the value is arguably smaller, at least for people like me who hate doing anything remotely complex on a tiny screen.

There is no reason to do anything complex on a tiny screen. The phone can stay a phone, except when you connect a keyboard and screen to it.

Nobody actually does that, turns out. Several manufacturers have the feature and it goes unused.

They do it wrong: Nobody needs to expand mobile apps to a large screen. There is only one company which does it right: Shrink desktop apps to mobile: https://puri.sm/posts/converging-on-convergence-pureos-is-co...

Total pipe dream. I like GNOME’s design but gtk and its desktop apps at large will never be appealing to mobile users, so I wholeheartedly disagree with you.

I already use a desktop Firefox and LibreOffice on my Librem 5. It's relatively slow but works sufficiently well with NoScript and text.

See also: https://puri.sm/posts/my-first-year-of-librem-5-convergence/