iphone not connecting to carrier (wifi does)

If you see No Service on the iPhone, see this for troubleshooting. If you see No Service or Searching on your iPhone or iPad - Apple Support

Wi-Fi calling does not connect to the cellular tower, that is using the wi-fi in your house for making calls. Part way down the list of troubleshooting is to contact your carrier.

Contact your carrier.

Make a call with Wi-Fi Calling

With Wi-Fi Calling, you can make or receive a phone call if you have a Wi-Fi connection in an area with little or no cellular coverage. Learn how to make a voice call using Wi-Fi Calling.

Make a call with Wi-Fi Calling - Apple Support

https://support.apple.com/en-us/HT203032