There really isn't any way to convert from a php web application to a full featured app for a smart phone. You can download the Android SDK and have a look through it. If you have any experience with Java you may find it pretty easy. Learning to code for Android is fairly tricky to say the least. I had a few app ideas and ended up giving up on them because I had issues getting to grips with it.
For iPhone is is very similar, there is an SDK that will run on Mac OSX, I don't have any experience with the Apple SDK so not sure about the level of difficulty.