Hello Foogin,
Thanks for getting back to us with those additional details. It looks like your bluetooth headset microphone is not working as expected during phone calls. We understand the importance of getting this issue resolved, and we'd like to help.
Do you experience the same behavior when using your iPhone's built-in microphone during calls?
The best way to isolate this issue further is to test using another brand of bluetooth or wired headphones to find out if it is a problem with your iPhone or your headset. Maybe a family member or a friend has one.
In the meantime, you may try to reset, and update your bluetooth headset. You can reach out to your headset technical support for assistance.
Also, check out this helpful link:
Set up and listen to Bluetooth devices on iPhone
Please let us know the results, and we'll go from there. Cheers!