It was a long time ago, so I don't remember. Phosh or Plasma. I tried to like Sxmo, but it was really unintuitive, unlike tiling WMs on Linux.
Fairphones seems OK, although for €549 I'll probably stick to a dumb phone and invest in a better laptop for now. I'm not saying it's too expensive for what it is, though - it's still a tiny computer with all kinds of periphery.
I just wish there was a version with a shitty camera for €50 less or with no Bluetooth for €10 less - you get the idea.
librem 5 is also an option. It is sorta expensive and weak but is the most capable.
https://wiki.postmarketos.org/wiki/Devices
right now im on calyxos but development has been paused for like a year