Ding ding ding! We have a winner.
First leap: That the child was crying. OP says in her first post that her daughter could see the kid was practically crying or about to cry. Over the course of 9 pages, this has been interepreted as openly sobbing, wailing, crying rivers of tears of anguish.
Second leap: That the tears mean the child was truly upset, not just being manipulative. I know a few kids (including my own) that cry to make the situation seem more dramatic or to make me feel sorry for them, etc. My daughter has an amazing number of deep emotional traumas, coincidentally when it is bedtime and she does not want to go to bed.
Third leap: The teacher is some control freaking ogre who refused to let him use the phone out of cruelty or ignorance. Perhaps the teacher, who unlike us has actually met this boy, knows the score just a teeny bit better than we do.
Fourth leap: That the child's absence had anything to do with his inability to use the phone, and that if it did, this is a negative consequence. We have no idea why the child was not in school - heck maybe he was being suspended for doing something really bad, and was trying to call home before the principal did to give his side of the story! Or, maybe his parents were just as outraged as you people and are keeping him home out of protest.
Either way, the fact that he was absent the following day doesn't change my opinion that the teacher did nothing wrong.
Schools deal with hundreds of children each day, all at once. When dealing with large numbers of children, there are certain routines and policies you simply have to put in place, or there will be total chaos.
I realize that YOUR CHILD is THE MOST IMPORTANT CHILD EVER TO WALK THE EARTH and it is OUTRAGE and INJUSTICE that they cannot do whatever they want, whenever they want. But when they are in a public setting, they will sometimes be forced to comply with the rules and wishes of other people.
This is life. Get used to it. Get them used it.