Ultimately, it should be a decision left to individual schools, not one of the government. I personally see no problem with students at secondary schools using their phones at break, or for educational purposes in lessons with the permission of the teacher. I feel teachers should be able to ask a student to stop using their phone in a lesson if they have no reason to be using it, though. The kind of education system the current government seems to be trying to create is seriously out of touch with modern times - I feel we should be focusing on improving the school environment to improve results (many of the UK's school buildings are in a rather poor state compared to those in northern European countries, Canada and the better public schools in the US) rather than discipline, and would roll back the majority of the post-2010 education policy if I was the education secretary in favour of a more liberal approach to school education.
I don't understand why our current government claims to be giving "more power" to schools via the creation of academies when they're becoming increasingly bureaucratic on issues such as this and on insisting that schools promote "British values". They recently encouraged primary schools to take part in singing a propaganda song (not officially described as such but that's blatantly what it is) called One Britain One Nation, which was far more reminiscent of something you'd expect from Russia or China than a democratic nation built on liberty and individualism.