car play when iphone 13 connected

Hi, having issues with a contact number this mobile number does not work on my car play all of sudden I can hear the dial tone when the person picks up the call all silence we cant hear each other. however if I put on loud speak can here the person perfectly. all my other contacts work fine not sure why this mobile number I'm having issues with have deleted the number reset the phone serval times getting the same problem. tried my work phone called this number and it works perfectly i cant managed to work out the problem on my phone to fix it!!!! thanking you in advance.