Have you taken a look at Ubuntu touch? I came across it while researching for my next device. From what I recall, it gives you a full Ubuntu environment on your phone.
Didn't go that route though because of the unavailability of the supported models where I'm at
Canonical supported versions were based on snaps-predating app framework (click packages). There were a couple of phones released with it out of the factory (bq aquarius 4.5 and meizu mx4) and a bq tablet, but rest of the supported phones use android kernels for hw enablement.
Ubutouch has forked the software when Canonical pulled out and even runs an app store, but I think the best hw you can get is Oneplus 6t and then mx4.
I used mx4 as my daily driver for years prior to switching to Android for the first time 3 years ago. While not the fastest phone, mx4 was usable (things I hated most were sharp edges and how it would register touches in my pocket, and then get locked for 10 mins because of wrong passcode).
To be honest, I quite prefer the Ubuntu Touch over Android (and Nokia Meego/Maemo is up there too, but Palm Pre WebOS takes the cake as the best basic phone UX I've experienced).
I think Mobian has the biggest potential to be the pure GNU/Linux system in your pocket, so I am hoping it'd get Unity included too.
Didn't go that route though because of the unavailability of the supported models where I'm at