@karenannwarwick it is possible that you have a mic issue. Try a headset with mic and see if that makes a difference.Try to use the speaker phone option since that uses the upper mic.
It is also possible that this is an issue with the flex cable connecting the SIM cardboard to the main board. For that you will have to teardown your phone and let us see all the boards etc. Consider replacing both of those.
Use these guides [[Topic:Huawei P30 Pro]] to work on it