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.
Actually your looking to increase shutter speed. The iPhone optics and shutter speed are way way way to slow to freeze action. As much as the new optics have done a nice job on improving overall picture quality the mechanics are not there to capture action.