I'm still boggled by the fact that a child has an iPhone!!
No, children shouldn't take phones on school trips for all the reasons mentioned on the first page of this thread.
As a school governor I have had to deal with a parent who sent her child on a trip with a phone, even tho' the head had discussed the issue with that parent before the trip, and believed that an agreement had been reached with that parent that she wouldn't send a phone.
Her daughter took the phone anyway, gloated to everyone else that she had her phone when they didn't, and then kicked up a TERRIBLE fuss on the first night when a teacher took it away for safe-keeping. The parent came into school on her daughter's return, effing and blinding at the teacher concerned (in front of children) and threatening to report us (we never found out to whom).
I dealt with it as a complaint to the school, and upheld that, if the school said "no phones", then no-one should take a phone.
The staff are there, in loco parentis, to care for your child on the trip. H&S rules demand that there are sufficient staff on a trip to manage all the children, and if there is an accident or other emergency, it is the staff's job to deal with it.
In our case, the head teacher (not on the trip), was in contact with a member of staff on the trip every day. As it happened, a grandparent of one of the children died while the child was on this trip. The head did offer to drive down to the location and collect the child to bring her home (parents decided to let her stay, not told about the death, as the funeral wasn't until the following week), so in a family emergency at home, the children can be informed, face to face, by a caring staff member, much better than a child dealing with a phone call to impart bad news anyway.