Has each phone been the same make and model?
Have you fitted a case which obscures the microphone?
Have you tried your phone's hands-free mode to see if that helps, @Shanelle?
You could check some of the tips in this Guide: How can I sort out my network issues? in case it is due to signal being blocked in parts of your house. Is there the same problem for a visitor to your house? If their phone is ok and yours not, swap SIMs with each other briefly as a test, see if the problem follows the SIM.
Not sure where the problem lies, at this point. Good luck!
I am having the same problem. People cannot hear me and I hear them perfectly. Calling on WhatsApp, FaceTime and Signal works fine. It just seems to be the O2 network. I have checked the SIM, I have switched the phone on and off etc. It is bloody annoying and been happening for 4 or 5 days.