Your kids could be silently behaving for hours on end, playing nicely, giggling, leaving you in utter peace and quiet, giving you the most idyllic of days.
Then their Spidey sense activates. You've taken out the phone and put it to your ear somewhere in the house.
Tantrum Engage! Suddenly, the only thing they can think to do is maul each other, screaming and crying the whole time. There's toy throwing, there's inconsolable sobbing, there's the inevitable child following you around looking for justice... "MOM, SHE _______ ME!"
Meanwhile, you just wish you had a kid-sized fly swatter. Why do they do this? Not only is it annoying to the tech person, teacher, interviewee (I'm a journalist), or anyone on the other end, it's mortifying.
I mean, is it their main goal in life to make me look like the worst parent ever at all times?!
There are a couple different ways you can go.
First, you can try telling them to stop. It won't work (probably) but you've got to keep that hope alive, right? I mean, maybe today's the day!
When that doesn't work, put yourself in another room. Lock the door if you must (my kids are five, so that's okay for me to do). Usually, of course, they'll hang right outside the door, screaming into it.
If that is the case, tell the person on the other end to hold on. Put them on mute to spare them as you go into the battlefield. Discipline your kids in the manner of a crazy person who's just been humiliated in front of some stranger they need help from. Put kids in room. Go outside. Walk a bit away from the house. Apologize to other party on the phone and quickly finish up.
The most important part of this happens after the phone call. My kids are actually finally getting better about phone calls after months of me doing this.
After it's over, go and talk to your kids calmly. Tell them the behavior is unacceptable and sometimes you are going to be on the phone and that you expect them to act appropriately when you are. This isn't going to work, of course, but after millions of repetitions of the same thing, it seems the kids are starting to get an inkling that the phone is not their enemy and they can just chill out when you're on it.
If you always do the same thing (I always go outside to the front porch when the call is important and verbally cue them that I am on a phone call and I'll be back in a minute) they get used to it via pattern recognition and do even better at laying off.
Alternately, never use the phone again.