PHP is on the server so it doesn't really matter too much as far as I can see - but it needs to be fast. For a mobile environment you may be more interested in the front end. So using responsive design with media queries and breakpoints may be more useful. You need to provide more info about what you're trying to do.
However, an "app" could be produced using "cordova" (commercial = phonegap) or an offshoot like "steroids". Lots of these about now.
The IDE Pritaeas. My webiste is written on PHP and i saw commercial online that Zend Studio is the best way to make your PHP website a mobile application. And thats what i am interested in. My website is fully functional. A few months back, just to get a glimpse of how to built an app, i installed phonegap, JRE, JDK i created a simple app (as it is shown on various video on the net) but i did understand how to connect the database and to use my already existing php files. I havent started using Zend but it says that uses Cordova. If you'd like more info diafol feel free to ask. Thanks