Hi Snipe_AT,
Make sure you have Wi-Fi calling enabled properly:
- "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."
You can find these steps along with other information that may be helpful, here: Make a call with Wi-Fi Calling - Apple Support
If you are referring to making a call with cell data completely disabled, we are always looking for ways to improve our products, so we encourage you to leave feedback here: Product Feedback - Apple
This is the best way to have your voice heard by our designers and engineers.
Cheers!