Hello there Yahya_ph,
Thanks for posting here on the Apple Support Communities! This is a place where other Apple users can submit questions or respond to others to help lend a hand. Let's take a closer look as we do our best to provide some additional insight.
We understand you're having some issues with audio quality only while on cellular phone calls. From what you've described so far, if the issue only happens with a cellular connection and not on FaceTime or with Wi-Fi calls, then the issue may be isolated to your wireless carrier.
If that's the case, have you already contacted your wireless carrier and had them attempt troubleshooting in their end? If so, what specific steps did they take?
Otherwise, we'd want to be sure to go over the rest of these general troubleshooting steps for similar issues: If you can't make or receive calls on your iPhone
If issues persist, and if you've already spoke directly with your wireless carrier after completing those steps, then you will need to contact Apple Support as mentioned at the end of that same article.
We hope this helps get you pointed in the right direction.
Take care.