Thanks @praveen@social.masto.host for helping me to get this work!
Instructions for the missing pieces are:
sudo apt-get purge pipewire-pulse(or disable the service which I didn't test)sudo touch /etc/systemd/user/wireplumber.servicesudo systemctl daemon-reloadsystemctl --user disable wireplumber.servicesystemctl --user enable wireplumber@video-only.service- reboot the phone
During looking for a solution I once deleted the users pulse audio configuration in .config/pulse while pulseaudio.service was stopped. Don't know whether this has been necessary to make call audio work.
A test call gave me audio without echo. Only the speaker button in gnome-calls seems to make no difference.
@praveen@social.masto.host @dos@librem.one @kannan@aana.site
I tried this solution (after testing the first time the echo in #trixie using #pipewire - it really is awfull 
) and found the speaker and headset working when using paplay.
The echo on calls is gone also - like any audio during calls is gone.
I do not remember how to fix the #audio during calls not working nor do I remember the place where I read about it. Help would be appreciated!
Best would be if someone would add echo-cancellation to #pipewire which is default in trixie. There's a slowly growing bounty on Open Collectives for that.
@dos @kannan For those who want to try, can install mobian-base, librem5-support and librem5-tweaks packages from https://people.debian.org/~praveen/mobian/ on your #mobian #trixie install. I have also sent merge requests to all 3 packages. Hopefully this can be shipped in trixie by default. Our bounty to fix this properly in pipewire still stands https://opencollective.com/dephcom/projects/pipewire-echo
#debian #librem5