For a crude audio test I called a viop.ms SIP account I have on my laptop computer. I then recorded the audio by selecting ‘monitor’ of my built in sound device. First you hear a OnePlus 6, then you hear the Librem 5 for comparison. Both were using my T-Mobile SIM, Cell data, ‘normal’ phone call. The L5 mic level was around 40%. Cell service indicator was showing about 3 of the 4 bars.
They both sound fine to me. The L5 isn’t worse in my opinion. Perhaps better.