Hi mnzib,
Thanks for reaching out to Apple Support Communities. It sounds like you're having an issue with the sound quality when on a call. We're happy to help.
We recommend starting with the steps here: If you hear no sound or distorted sound from your iPhone, iPad, or iPod touch speaker If the issue continues, check out the steps here: If the microphones on your iPhone aren't working this includes testing the sound in a Voice Memo.
Also, does this occur with both Wi-Fi and cellular calls? If you're unsure, we'd recommend testing between and in a different location to see if the issue continues.
We'd also recommend checking into any interfearance with Bluetooth accessories. If needed, the article here can assist: Resolve Wi-Fi and Bluetooth issues caused by wireless interference
Should the issue remain, reach out to Apple Support
Cheers!