Victor,
Answering to the question "Why do u need the PhoneGap.js file?" the PhoneGap.js is used to make the bridge between the JS that your putting into your Outsystems app and the native code that is needed to run.
On an OutSystems app, you don't need to add the EventListener JavaScript, you can check if you are in "PhoneGap mode" by passing a parameter like ?IsPhoneGap=True, in the URL on the html file loader you add to PhoneGap zip, and then just load PhoneGap.JS when you need to use it.
To trigger the the camera, use a button or a link (with the onclick extended propertie, if you don't want to submit don't forget to end with a "return false;") to call the java script function that gets the picture and then you can associate the picture URL(Binary Data) to an element or pass it to ServerSide, by using an intermidiary element (like an input).
On attachement you can find and example that is using the CameraCapture plugin, and an implementation of the plugin in the PhoneGapIntegration. Let me know if it helps.
Regards,
Elísio