Hello Me2929,
Are you using any accessories, such as headphones, with the iPhone when the call disconnects? If so, try disconnecting any accessories to help rule out any possible issues being caused by the accessory.
Be sure to also check for any updates for the iPhone, as that'll ensure it's using the latest improvements and fixes. The latest version at the moment is iOS 16.6 for reference. This page can help with updating, if needed: Update your iPhone or iPad - Apple Support
Does the issue seem to occur on calls with particular contact(s)? If so, try checking with the other person to see if they're experiencing disconnects as well when they're on calls with other people. That can help to see if it may be caused by the other person's end.
Cheers.