Should a parent hold a conversation with their kids while on the phone with another adult/parent??

I was always told not to interrupt my parents or anyone for that matter on the phone unless it was an emergency or important enough to interrupt....
While talking with my good friend on the phone and having a great "catch up" conversation with them - then - in walks their child and they begin having a conversation with each other about things that could have waited 5 more minutes for us to get off the phone. They come back on line and say and what were you saying????