I have the same problem unfortunately. The most annoying that it went down week after warranty expired and I was proposed to purchase new phone with “discount”. It seems that the problem started even before - sometimes it was possible to conduct a call only after the 4th attempt to be heard. As this was not occasionally - the problem was considered as carrier issue. Only now Apple service confirmed that these were phone issues unfortunately as the warranty expired they cannot help despite provide the new phone for better price. But the problem started before it expired!!!!