In short, yes, you can do this. Phonegap is html/js/css packaged into a web container in a native app. However don't expect your site to just instantly work perfectly within a Phonegap app, you'll need to do some re-packaging. Check out the docs and give it a shot.
Also, don't expect Apple or Google to approve you app if it's just a website wrapped into a mobile app, they explicitly forbid that, you app should provide some native functionality through the Cordova plugins