Answering calls on iPad Pro

Is your phone set to Do Not Disturb? The slide switch on the left will only silence the ringer (and vibration, according to your wishes), but not the visual alert. Do Not Disturb will suppress everything.

Are you engaged in a phone call on your iPad when the new call comes in? iPads, even cellular enabled ones, only handle voice calls as a slave to your iPhone. When a second call comes in, the device engaged in the first call needs to put the call on hold to handle the second one. There is only one voice path available on the cellular network.

Be aware that unless your Cellular carrier supports - and you have enabled WIFi Calling on both your iPad and iPhone - then all calls are effectively controlled by your iPhone.

If using WiFi Calling features provided my many full-service carriers, it is usually possible to simultaneously handle multiple calls using the same cellphone number. With WiFi Calling, the iPad (and iPhone) can route calls via WiFi and the internet - rather than rely solely upon the Cellular network and proximity of the iPad to the paired iPhone. Effectively, the two devices become independent of each-other, but calls are billed to your cellular number.

I hope you find this additional information to helpful.