Phone call stops and makes weird sound
Instead of the other person's voice during the phone call on the iPhone, the call connection sound and the sound made when the call is disconnected are mixed and played repeatedly
iPhone 15 Plus, iOS 18
Phone Switched off, Not Answering, Engaged, Out of Network coverage area, or Not reachable are messages conveyed to your caller from your Carrier's tower and not from your iPhone.
When a caller calls a number your Carrier's network tower tries to reach you on your device and tries to get the status of your mobile. What is fetched and what is recorded is totally by the carrier's server.
Please contact your Carrier.