I’ve had this same idea, down to the functionality and even using a Samsung FlipZ (I believe it’s possible FlipZ phones support Linux) foldable chip to achieve it!

I was just revisitng the idea yesterday but building a foldable clamshell Gameboy SP like case instead.

IMO you only really need a 4-inch square screen. Now I know it’s possible. I would even take a 4-inch screen device without a keyboard or cellular modem.

ctrl+c ctrl+d ctrl+v are all too important for me to drop any keyboard.

but, i did get me a tiny 6 key and a knob keyboard i can bring around with my phone, and it gets 95% of what id otherwise use my keyboard for