Your phone is ringing and your daughter picked up the phone but she hasn't answered the call. Then do you ask her:
Who is it?
or
Who are they?
And when she tells you, would she say:
I don't know who it is"
or
I don't know who they are?
If none of the above isn't natural, then what is it?
Best Answer
The question (at least here in the U.S.) is:
It may sound impersonal, but it's idiomatic.
As for how one might answer that question, that could be done in just three words:
(Or, your daughter could string all three of those together for a nine-word reply.)
As to how to phrase it in a longer form, I think you nailed it in your question:
That's exactly how I would say it: