Hi @DavidJ2 !
Does this happen with every person you speak with?
Also, did you notice a difference when you put the call on speaker?
It could be an issue with your device's microphone, but it'd be best to first make sure that it's not caused by the network connection itself.
A good test for this is to try your SIM card in another phone, to see if the same thing happens.
Keep us posted!