Poor call sound quality, how can I fix it?

My passport audio quality on calls is poor the sound is distorted and I have to turn down the volume so that it is possible to understand what is being said. If I put the phone on speaker I dont have the problem at all and its very clear. Can anyone suggest a solution?

Thanks

short of changing the OS, i think you will just have to adjust the volume to get better sound qulity

Run the audio tests in BBVE. It won't fix your problem but may give you more insight as to whether it is hardware earphone malfunction. Any hard drops or fluid exposure?

May not make a significant difference but in Phone Settings you can also toggle the bass or treble levels to improve clarity.