what version are you on? this was a recent fp6 call audio thread (and in there another audio thread linked) that said things seemed to have improved with v3.2
I’ve been having the exact same issue myself since I bought my FP6 with /e/os in September, I’m also running version 3.2-a15-20251022539003-official-FP6 but the problem was there before. From what I can see here it seems like they might be releasing a bugfix in the upcoming version 3.3, although the thread is mainly about bad quality of the audio while recording videos they also mention phone calls and I think the issues are related. I’m waiting for the new release to check if it’s solved.