I have been using the officially supported Sailfis OS on Sony Xperia devices for years as my main device:
https://jolla.com/sailfishx/
The idea is you buy one of the supported Xperia phones, buy a Sailfish OS license and flash it on the phone. The license you bought pays for continued software updates (new features & security fixes) as well some external software they integrate (predictive typing support & android app emulation support). Yeah, if the native Sailfish OS apps are not sufficient for you, it can also run most Android apps via an emulation layer.
So while Sailfish OS is not fully open source unfortunatelly, it's at the moment IMHO the best mobile Linux distro available on easy to get modern hardware.
Ideally over time fully open source distros and more open hardware take over but till then Sailfis OS can serve as a good "bridge", AZ it has since the Jolla company taking care of it was started by the ex N900/Maemo/MeeGO crew.