Why can't I hear others after adding them to a call on my iPhone 13 Pro Max?

So this has been going on for a very long time. I chat with someone and then add the next person to the call. However, I am unable to hear them, but they can hear me. If they hang up and call me I still can't hear them. I need to shut down my phone and restart in order to call them successfully. At one point we thought it was related to the length of time I spoke with the first person--that does seem to fit. I've noted that most times if we chat for more than 4 or 5 minutes it will happen when I try to add the next person. BUT it isn't that way 100% of the time. As you may guess this is getting really old....any thoughts?

Details: iPhone 13 Pro Max, up-to-date

[Re-Titled by Moderator]

Original Title: When adding a person to a call, I am unable to hear them but they can hear me.