One comment mentioned Jolla. Another currently available option is [FuriLabs](http://furilabs.com). It runs atop Hallium/etc but you are effectively still able to daily drive a mobile Linux shell and contribute to the ecosystem if you want to see it grow.

Now with that said: so much work has gone in to Android (and by extension, Graphene) to improve on power usage/security/etc that I'm not sure I'd bother to actually run a mobile Linux device. The juice just doesn't feel worth the squeeze.