Phosh is definitely more polished and an attempt to make gtk mobile friendly. I actually prefer gnome-mobile for testing purposes. It’s exactly like gnome-desktop and apps are opened each in an workspace, which is an impressive solution. It also needs more resources, and its not recommended for the first pinephone.

I know about Geary. But it’s not the same as a complete Thunderbird install. There I can use my smime/openpgp certs and tags are also synchronised.