There’s an upcoming pocket-sized computer that has attracted attention, the Mecha Comet.
It has a touch screen, runs Linux, has an external interface for mounting expansion modules, and is designed for user repairs and upgrades.
Here’s the current description: Mecha Comet - Modular Linux Handheld Computer powered by Open-Source Software
Today, there was a livestream where they announced improvements to the design: https://www.youtube.com/watch?v=QssMPn3K_HE
There will be a Kickstarter campaign later this year.
I have no affiliation with this project. I mention it just because I think it’s a neat design, and others might be interested in it.
Oh yes, with an appropriate expansion module, you’ll be able to use it as a 4G phone, at least, and maybe 5G.