today in car while listening streaming music using some DAC usb-c → Jack i got phone-call and the caller did not hear me, i had to unplug dac.
it looks like the phone switched Mic to input from DAC even there is no microphone connected (only line-out to car aux input, or just headphones without mic)
i have more DACs variants here, but all failed for phone calls except Apple DAC
so i recommend to use Apple DAC with silent volume fix (updated for Jolla Phone)
@rainemak a little ironing on switching input to dac will be needed , maybe option in Settings → Sounds → Allways use internal MIC or something like this would be fine enough, or ability to enable/disable external microphone in same way as using earspeaker/loudspeaker during phone call