All iPhones ringing - how to turn off?

I have 2 iPhones - 1 person, 1 for work. The purpose of having 2 iPhones is so that I can have a life, without being interrupted at night and on the weekends by work calls.

I updated all of my iDevices last night to iOS 8 (iPhone 4s (work), iPhone 5s (personal) and iPad Air). I just got a work call on the 4s, and noticed that my personal iPhone (5s) also rang from the same contact. How do I turn that off? There is no sense having 2 iPhones, if my personal 5s is now going to ring whenever the work 4s gets a call.