Don't remember if I mentioned this here, but I (finally??) came up with a good response to HS students "I have to take this call. It's an emergency" in the middle of class.
I tell them "of course, if it is an emergency, you need to take it. I care about you, so I'll call home later today to check that everything is okay."
"I care about you" is phrased as appropriate for our relationship and the age of the student.
Ofc, since I came up with this, I have not had to use it.