The problem of a Linux phone is not the hardware, it's the software. Are you doing to run a desktop OS on it? No. And if you want something like Android but not Android itself, how are you getting enough quality apps made? What about things like banking apps, who is going to port those?

While I would like a pure Linux phone, I think the only reasonable course of action is Android with something like Samsung's DeX on top. Maybe that is something they could do, but I don't see this happening any time soon.

You may be interested in this : https://wiki.postmarketos.org/wiki/Category:Interface

Those interfaces exists and are pretty mature compared to their current marketshare which is near zero.

What is missing though is a real developer/hacker community around Linux on mobile because even installing Linux on a smartphone is a huge PITA starting by being lucky enough to own or find a compatible terminal. Something from the Raspberry PI foundation with official support, clear and easy to buy would be absolutely groundbreaking and could became THE platform to develop Linux on smartphones.

Linux is really not that far behind, it just lacks a real community.

Idk, it's not obvious that you shouldn't run a desktop OS on a phone. What's yourr main issue with that?

You could run android apps in a Android container as needed.

I personally would very much like a device that's a pocketable desktop-OSed computer that can make phone calls and 2FA.

They just need to add slot for sim and 4g/5g support, you leave the rest to the community to play with, there is Ubuntu Touch, LineageOS, SailfishOS, postmarketOS, Plasma Mobile, Tizen, KaiOS, Mobian, PureOS, GrapheneOS, CalyxOS, /e/OS, Replicant, Droidian, Maemo Leste etc. - if there would be hardware available, people would play with it.

A good phone is an order of magnitude more complex than this.