P.W.
I just want to interject...... sometimes a cell phone is appropriate for an 11 year old, especially if they walk home from school or have to wait alone after school. Rules can be imposed where it is taken away at certain times....like after school or after a certain time.
I., tell your daughter you love her and that means protecting her. Tell her you aren't doing these things to be mean but because that's what a good mom does. You have 5 kids......so you probably remember that when they start puberty times get tough. Sounds like your little girl is there already.
Keep your rules without anger. Tell her you love her and that you are sorry she isn't happy with your rules, but keep your rules. Hopefully it will get better by the time she is 15.
:)