You were talking on the phone with your mother while riding in the car with your sister. You suddenly weren't able to hear anything, so you hang up and say this.
We got disconnected.
When you're talking on the telephone to someone, and the phone stops working for some reason, it's called "getting disconnected".
You can say that the phone got disconnected. However, people more often say that "we" or "they" got disconnected:
Did you get disconnected?
You can also "get disconnected" when you do a video chat on your computer.
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