This was a feature on iOS8 and it's the phone guessing what you want to do based on time and location.
For example, mine is always music when I get in my car so I can choose what I want to listen to but when I arrive at work it changes to Facebook because I like to have a little browse before I start my shift. Right now, at home the icon is Safari because it's not unsual for me to do some browsing before I get out of bed, when I went shopping last week it was Starbucks because it didn't know what to do with itself but Starbucks was just around the corner.
I hope that helps. The more you use your phone in different environments, the more it will learn about you. You'll probably notice pretty soon that if you drive, your phone will have learnt where you work and will tell you how long it takes to get there once you've sat in your car.