I was a supply teacher (as was the victim) in difficult schools in Bradford and Halifax. I worked for many years at this very difficult job and was one of the only 2 Supply teachers (in the UK) awarded the Threshold qualification when it was introduced. That's an intro.!
I have also faced pupils threatening physical violence, including one girl (I think she had been sniffing glue) who stood in front of me, weaving, with a pair of opened scissors. Teaching is not the peaceful job many still think it is. I am so sorry for this poor guy. You are damned if you take the phone off them and damned if you don't and they disrupt.
Unpalatable as it may be to some, this teacher was black - and Asians generally hate blacks. I'll happily explain how our school lost all its good black athletes when the Asians invaded the areas they had called home.
Before anyone starts to shout 'Racist' at me - - I'm telling the truth as it has unfolded before me. I really hope that the teacher is OK.