It really depends how you can control your phone. Start from there and work backwards. I suspect once you've identified a particular method that will work with your phone, it would be straightforward to provide an arduino interface. So search for a way to control the phone, particularly with an open source app.
More often an android/arduino combination is to put the control on the phone, and use the arduino as a driver/sensor, such as Android-Arduino BTCOMM do-it-yourself (DIY) Shield Versions 1.0 and 2.0 - BuildCircuit.COM