Pop up in lieu of ringing

I have a Nexus 5X and my phone just started the most unusual activity. For whatever reason my phone does not ring but a popup occurs when I receive a call. Any ideas please Thanks

This can happen (if I recall correctly) if the calling number has already been identified as spam and/or is on your block list.

Other than that, are you sure you don't have the ringer volume turned all the way down? :)

Thanks It is the spam situation you describe