Comment by veonik

WiFi calling is multicast, I think, so your phone just basically broadcasts it to the network and every device will see it, though only your router will actually do anything with it.

There's examples of WiFi calling causing this type of issue, described as a packet storm. For example, here's a reddit post with similar symptoms you're describing. https://www.reddit.com/r/networking/comments/3g31mc/iphone_w...