You should edit '/usr/share/alsa/ucm2/simple-card/VoiceCall.conf.leste' And modify Code: cset "name='Earpiece Playback Volume' 100%" with let's says 70% instead of 100%. Then reboot. If it works (i don't have any Pinephone to test myself), then we can make (or ask for) a PR on github to change this default value.
cset "name='Earpiece Playback Volume' 100%"