Voice delayed and muffled during calls

Hi, I’m a pretty new user to FCC - I’m mostly using it to record calls between me and one client. Unfortunately, the client has complained that the sound is somewhat muffled, and I’ve noticed a delay between when I speak and when they hear me (and vice-versa). We haven’t had these problems when talking on the same phones in a direct phone call. Does FCC Pro improve these issues? Any suggestions on what to do to help with these issues? Thanks for your help!