Can I use iPhone mic with AirPods as headphones while on a call?
No, I would do an A / B test to see if wired headset is higher quality that the Bluetooth one. You could even do that call with Apple Support so they could hear the difference and set up a repair if your bluetooth microphone is wonky.
Dropping AirPods can happen easily and internal damage can be both hidden to you and cause them to lose massive amounts of quality or just sound buzzy.
Before you call support, check the mesh openings (all of them) with a magnifying glass and look for signs of cracking.
P.S. always having wired headset is my conference superpower. Being able to quickly get perfect sound on a call is well worth the expense and hassle for me when sound quality matters.