Why my voice is breaking on video calls over iPhone 11

Whenever i use video calling either on WhatsApp and FaceTime, i face a serious issue, my voice gets broken in 60% of the video calls and people can not hear my speech properly.

I gave my phone to 2 different authorised service centres and they simply updated the operating system of my iPhone 11 but I’m still facing the same issue.

This problem is only on Video Calls, not on audio calls and cellular calls. My phone is just 2 months old and it’s under warranty. How can i get it replaced?