Unfortunately, that’s not the issue. I and other people here in the forums have had the same problem, as well as a couple of XDAforums and Reddit users (which I won’t link here, but they can be easily found by searching).
For me, two different fixes seemed to work, but only for a short while:
Making an XMPP and/or SIP call restored normal functionality, but later the problem returned.
More recently, reinstalling the same build brought back the audio, but that didn’t last, either.
Call audio is still not working on my Sony.
EDIT: I should note that I’m using a different ROM now (not /e/OS), and although the audio was restored when I switched to the new ROM, the problem eventually returned.