Poor mic audio only on phone calls

Seeing a similar problem reported on this forum I followed the directions of replacing the Lightning Connector Assembly which includes two microphones and the headphone jack. This did not fix my problem. The problem is when on phone calls my outgoing audio through the local microphone is very muffled and low in volume. If I plug in the earbuds with mic then it’s OK through the headphone connection. If I switch to speaker phone mode then that’s OK too. I can record good audio while shooting video (both front and back camera/microphones) and can record good audio using other apps such as voice memo. But try to make a call then I have to use speaker phone or use headset which I don’t always have with me. I purchased the Ifixit Pro Tech tool kit and the replacement lightning connector assembly, installed it, and still find the same problem. While the phone was apart I made sure the mic ports were clear of debris. What else is suggested I try?