As far as I know, the only “stable” linux phones are the Pinephone and Librem 5. The former runs hot and is painfully slow and the librem is very expensive for what you get. Some android phones can be reflashed but there are always core hardware features missing like camera, usb and GPS. I wrote this comment on my Oneplus 6 running postmarketOS, so you can make it work if you accept the shortcomings.