Do you have a wired headset you can hook up to the passenger intercom, so you can test if voice is getting into the mic circuit? Less likely you have it, but also will test, through a voice command GPS or GPS as a speakerphone that is hard wired to the mic.
Voice is supposed to be live in the intercom all the time (when that circuit is on), and only goes to the CB when you push the PTT button. (you are pushing that, right?)
Test will tell you if it is a CB problem, or a getting anything into the mic circuit problem. Which someone else will have to help you with, because I'm out of Schlitz.