When receiving a phone call on iOS 9 while you're in the middle of something, there are only two ways to interact with the presented screen. Either you wait until the other person hangs up, or you decline the incoming phone call. The first option is not useful when you're pressed for time and the latter is considered impolite. Additionally, if you're receiving these calls continuously, this could render your device unusable. That is my take on solving this problem in an unobstrusive manner.
