The smallest that is actually somewhat usable is the Pixel 3a. I've ported Mobian to it, but it's getting old and isn't the fastest device.

I'd like something smaller, but there isn't. So now I use a Fairphone while constantly complaining about it's size, not a perfect solution, I know. xD

Commodore is launching a hybrid phone between a dumb- and a smartphone with a version of the Sailfish operating system. It’s a flip phone with a retro look:

Commodore Callback 8020

Problem for Linux on phones is ARM limitations require a unique device tree for every OS deployed per device.

When I retire to Asia next year I'm considering just getting one of those simple feature phones sold in India which has Firefox OS. Limit myself to Vox/SMS/Email.

I'm showing my age but I fondly remember those lipstick case Nokia's from back in the day. Couldn't get much smaller than that.

It's not Linux, but it is more privacy focused: Commodore callback 8020

i have a xperia xz1c and it runs lineageos, small enough for me.

there's xz2c which has a unofficial sailfishos port iirc

Maybe the smallest Sony Xperia with Sailfish OS?

Dunno, but watching with interest. The Brax3 is massive, and even most of the stuff Graphene runs on is too big for my taste

I have a King Kong Mini 2, it's 4". Not shre what the Linux situation on it would be though

i use a Moto Fold 50u for that reason, I can do a fair bit of stuff on the external screen (reply to Signal messages, read emails etc) and then fold it out for more

caveat: it's a Moto with Android, i don't know if future Moto flips will have graphene support, or it's just their future signature series.