For moving objects you need to 'pan' the camera along with the object. It usually takes a shutter speed of 1/250th to freeze a moving object. Depending on how fast it's moving of course. I'll have to look at the top shutter speed of the iPhone.
If you follow the object, like a moving car, with the camera and take the photo it should have the car in focus and the background blurred. It can take some practice but is a great effect when you get it right.