Hey, AndyLester82,
I see that you've been having some issues receiving phone calls, with the audio sounding slowed down. I'm happy to help you with this.
To begin, many call audio issues could stem from the strength of your network connection. Have you checked to see how many bars of service you have when this occurs? It's also possible that you may see 'No Service' or 'Searching' at times like that. If that is the case, this article has a lot of really good information - including troubleshooting steps - that should prove helpful: If you see No Service or Searching on your iPhone or iPad.
Those are the steps that I would recommend starting with, and seeing if the issue resolves itself after trying them.
Hopefully this helps get you back up and running.
Cheers.