POTS is not POTS any more. Anything other than possible last mile is now digital, with lowest possible if not lower bitrate and old codecs. And that extends to mobile.
It really should be AMR-WB or even AMR-WB+ by now, and EVS if you are on VoLTE.
EVS are very good at 16-32Kbps bitrate, possibly better than even Opus. But generally speaking Social Apps uses higher bitrate you get better quality. Although latency tends to suffer a bit.
