I'm really liking the upgrade to trixie, now that I have a work around to fixing echo in calls - I went back to pulseaudio as @dos suggested it would be simple. Though with one mistake in coping systemd user-presets to wrong directory (even though I thought I disabled wireplumber and pipewire-pulse, it was not actually disabled), I had to do a lot of troubleshooting as all my audio devices just vanished! Thanks also to @kannan who suggested to remove pipewire-pulse.
@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
@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.
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.
I wanted to try #Mobian #Trixie on my #Librem5 again as I got a way to go back to #pulseaudio to as a work around to missing echo cancellation support in #pipewire (Thanks to @dos ). So I went ahead and ran the usual apt dis-upgrade way (in hindsight, may be gnome software was a better option). But I got locked out of the session as upgrade was progressing. So I had to force shut down and then use #JumpDrive to repair it from my laptop.
I documented it in #debian wiki
https://wiki.debian.org/InstallingDebianOn/Purism/Librem5Phone#Using_JumpDrive_and_qemu_to_get_emergency_access_to_your_system