GuiltyPleasure just reading some comments here! It's very interesting. It's curious some people don't see it as the schools fault, or feel it is your dd's mistake, even though they caused your dd to be late and miss her bus by taking her phone, not letting her collect it 5 minutes early, and then having it in an accessible place!
If 15 year olds are so much like adults, as some seem to suggest, can we imagine how this would fly at work, if as an adult I was not allowed to use my phone at work and due to a similar kerfuffle I was left stranded at work! I'd be pretty pissed off.
Plus this 2 mile walk to town or 8 mile walk to home sounds like where I live, country roads, no pavements, 50 mile speed limits in some places o traffic travels fast, so walking around is just not so easy.
Can I just ask, as someone else did, and I did not see the reply, why was it a problem if it was lunchtime? It may help to clarify whether kids can use their phones in the lunch break, because if they can, then the school was at fault to take the phone away.
I think (in your shoes) I would contact school and just say it had inconvenienced you that the school staff had not been able to return dd's phone in a timely manner, and you know (if it was definitely a rule break for dd to look at her phone on school premises or whatever - if it is the case) that your dd was at fault but kids all make mistakes/break rules and the school system should be able to accommodate this without causing further issues for the pupil/her parent.
Plus it's all very well to say leave the phone at school but maybe she thought you would be cross if it were left at school!