WiFi calling

Welcome Leeann267,

That's correct. You can make a call using Wi-Fi only, when you do not have access to good cellular signal or have no service (with a supported carrier): Make a call with Wi-Fi Calling - Apple Support

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.

To use Wi-Fi Calling, you need an iPhone 5c or later on a supported carrier.

Place Wi-Fi calls from your iPhone

Turn on Wi-Fi calling in Settings > Phone > Wi-Fi Calling. You might need to enter or confirm your address for emergency services.*

If Wi-Fi Calling is available, you’ll see Wi-Fi after your carrier name in the status bar. Then your calls will use Wi-Fi Calling.

* When cellular service is available, your iPhone uses it for emergency calls. If you turned on Wi-Fi Calling and cellular service isn't available, emergency calls might use Wi-Fi calling. Your device's location may be used to aid response efforts when you place an emergency call, regardless of whether you enable Location Services.

Hoping this helps out, take care!