If, like me, you're someone who gets uncomfortable talking on the phone, you're probably superthankful for the iPhone's accept/decline button when you get an incoming call. But you're probably also confused as to why you only see it sometimes. Most of the time, you may have noticed the slide-to-answer feature.
Much to the relief of introverts everywhere, the reason behind these changes has finally come to light, courtesy of Business Insider. Instead of a complicated cause, such as discrepancies between iPhone and non-iPhone users' calls, the answer is simple. If your iPhone is unlocked while receiving a call, you'll see accept and decline buttons on your screen; if it's locked, you'll get the slider. Aha!
I tested it out by having a co-worker call me twice. Sure enough, it worked the way it's supposed to. Case closed, everybody.