If at any point, he sounds angry:

"You sound angry. Is there anything you would like to talk about?"

If his response is YES, listen and validate.

If it is NO. Just remember it is his Anger to deal with. Get back on kid talk.

"What is best for my kids is best for me"
Amor Fati
Link to quotes: https://www.divorcebusting.com/forums/ubbthreads.php?ubb=showflat&Number=2879712