Perform these Basic settings

Disable Focus Mode: 

Swipe down from the top-right corner of your screen to open Control Center and tap the Focus button to turn it off.

  • Turn off Silent Mode: 

Check the physical silent switch on the top-left side of your iPhone; if it's orange, the phone is in silent mode.

  • Verify Silence Unknown Callers: 

Go to Settings > Phone and ensure the "Silence Unknown Callers" feature is turned off.

Adjust Phone App Settings

  • Check Call Forwarding: In Settings > Phone, ensure Call Forwarding is disabled.
  • Ensure a Ringtone is Set: Go to Settings > Sounds & Haptics and make sure a ringtone is selected in the "Ringtone" setting.

 

Troubleshoot with Network and Software

  • Restart Your iPhone: 

A simple restart can often resolve temporary network or software glitches.

  • Toggle Airplane Mode: 

Turn on Airplane Mode for a few seconds and then turn it off to refresh your network connection.

  • Update iOS: 

Outdated software can cause bugs that affect call routing. Check for updates in Settings > General > Software Update.

  • Reset Network Settings: 

If the issue persists, you can reset your network settings in Settings > General > Reset to restore default network configurations.