Yeah, I've been watching the mobile Linux space with interest but it's definitely not in a place yet where I would consider using it as anything more than a novelty. The PinePhone is a neat little piece of hardware but no way it can replace my LineageOS phone right now.
I was vaguely wondering how hard it would be to use a GNU/Linux laptop as a phone. If you always carry a laptop, that's more-reasonable than it might seem, and that opens things up hardware-wise a lot. There are at least three obstacles:
The touch-oriented app infrastructure is stronger on smartphone OSes.
Laptops aren't as good at idling power-wise as phones. You want to be able to listen for calls without consuming a lot of power.
Apparently, while you can get 5G modems for laptops, getting one for a computer that can do voice service is not an option today. You can do VoIP or something, but I suspect that you're looking at a latency hit then.
Can they at least handle texting? A lot of services require SMS-based 2FA (insecure as it is) these days, so a phone that can't receive texts is a complete non-starter.
I don't know that off-the-top-of-my-head, but I would guess that with normal voice service the modem may well also handle texts, as at least historically, I believe the SMSes went over space in some sort of command channel separate from the per-active-phone timeslice reserved for voice.
However, you could hypothetically get SMS service and relay that to a your laptop-phone over IP from some service that provides VoIP service. With SMSes, unlike with voice, the latency shouldn't really matter.
It seems to me that that might seriously deter third-party Android distributors—AFAIK most do not ship stock Google apps for all the basic utilities, they only ship the auxiliary ones like Gmail or Docs.