Use FaceTime with your Apple ID
Turn on iPhone Cellular Calls on your iPhone
Make sure your iPad and iPhone use the same Apple ID
Connect both devices to Wi-Fi
On iPad, go to Settings
Tap FaceTime
Turn on FaceTime
On iPhone, go to Settings
Tap Phone
Tap Calls on Other Devices
Turn on Allow Calls on Other Devices
Turn on your iPad in the device list
Open FaceTime on iPad
Tap New FaceTime
Enter a contact name, phone number, or email
Tap Audio or Video
Use a calling app that supports iPad
Install a VoIP app from the App Store
Sign in to the app
Allow microphone permissions
Start a call from the app
Use Continuity with a nearby iPhone
Use Wi-Fi calling through supported carrier apps