Personal BYOD - filter contacts

Hi

We are a college and need to enrol BYOD devices to meet CE requirements, which includes staff personal mobiles for when they access email etc.   Android works really well with Personal/Work split, iOS devices, not so well.   

We've noticed that when a personal phone is enrolled and they search contacts, it is pulling back all contacts within the tenant and there is no way to switch this off when just using on a personal basis.   I need to filter this to search staff only, excluding students.    How can this be achieved.

Thanks