Phonegap produces a static application composed of a native webview and code to expose the functionality of each system to a javascript API. Your HTML/CSS/JS code will be packaged without significant changes along with the native Phonegap system and will run like any other web page, but offline and with access to native functions. The engine that will actually run your Javascript depends on each platform.
Session Overview of documentation:
The application itself is implemented as a web page, named index.html by default, that References whatever CSS, Javascript, images, media files, or other Resources are necessary for it to run. The app executes as a Webview Within the Native application wrapper, which you Distribute to app Stores. For the web app to Interact with Various device Features the way Native apps do, it must also Reference a Cordova.js file, which provides API bindings.
Free translation:
The application is implemented as a web page, named index.html by default, which references any CSS, Javascript, image, multimedia file, or any other resource needed for it to work. The app runs as a Webview within the native application encapsulation, which you distribute to app stores. In order for the web application to interact with the various features of the device in the same way that native applications do, it must also reference the file Cordova.js, providing connections to the API.
The native app it generates is basically a browser. The html/css/js code runs in this "browser".
– bfavaretto
As generated some doubts, I edited to try to facilitate the understanding. If you did not give better understanding to your intention, please reverse or reissue.
– Maniero