Basically what TGS & FPS said.
Get an unlocked pixel from google. They often run a 50% off sale on black friday. Put something like calyx or GrapheneOS on it.
https://calyxos.org/
https://grapheneos.org/
https://securechatguide.org/favorites.html
https://www.securemessagingapps.com/
But I am still awaiting better Linux based phones.