Hey sudeepthi,
Thank you for using the Apple Support Communities! We understand you're having an audio issue on video calls only, but regular phone calls are fine. Let's help.
With this happening only on FaceTime and WhatsApp video calls, have you checked your FaceTime audio settings? If you're using iOS 15 and an iPhone XR or later, this will be relevant: Change FaceTime audio settings on iPhone.
Does this audio issue only occur when you're connected to cellular data? Or, are you connected to Wi-Fi when the issue is present?
Do you use a Bluetooth or wired headset with your iPhone when you're on these video calls? If so, when you stop using the headset, does the issue resolve? If you're not using a headset, can you try one to see if it helps?
Keep us posted. Regards.