Hi tlfmd,
To disable calls entirely on the iPad, you can turn off Calls from iPhone. You can see how to disable the feature here:
Make and receive calls on your Mac, iPad, or iPod touch - Apple Support
"To stop getting calls on one of your devices, just turn off the Calls from iPhone setting on that device. See the setup section above for details."
Calls should be arriving on all devices when the feature is enabled. To troubleshoot the feature, you can test after turning off Allow Calls on Other Devices on your iPhone, and then turning it back on.
To do so, follow these steps:
- On your iPhone, tap Settings
- Tap Phone
- Tap Calls on Other Devices
- Turn the feature off
- Wait 30 seconds, and then turn the feature back on
If calls continue to only arrive on your iPad, then reach out to Apple Support directly for further assistance with the behavior. You can use the following link to reach out: Contact - Official Apple Support
Kind regards.