The OnePlus 6 and OnePlus 6T seem to have some microphone quality problems - TalkAndroid.com
Oneplus 6 Sound Problem Music Loudspeaker Mic Not Working Hang On Call Solution[Hindi]4K - YouTube
C-TYPE In-Ear Headphones Earphones for OnePlus 6t ,OnePlus 6 t , OnePlus 6 T Metallic C Type Earphones with Mic and Volume Controller, High Bass Headphoens for Mobile, Wired Earphones | Earphone
Microphone for OnePlus 6 by Maxbhi.com
HITSAN INCORPORATION for oneplus 6 oneplus6 A6000 A6003 Microphone mic Bottom Board Auxiliary PCB Circuits and Audio Jack : Amazon.in: Electronics