Okay so in order to convert it first you are going to have to know Objective-C because that is the only language that is allowed on the iPhone but assuming you know that here are the steps you can take in making a conversion like that.
*Make sure that any outside information the application retrieves is either a) In a REST api you can use the new WebApi in fact I am using it right now and it works like a charm. Or b) Any script src= tags are converted to local files on disk. So if you had script src="My awesome css" make that file a local file on the phone.
*Next take any views and decide where all of their API calling code is. Make not of that and then get ready to be moving that code.
*Once that is all recorded startup a phonegap project and get rid of any extra .index files or anything you don't need.
*Create your applications PhoneGap plugin. Have the OBjective-C plugin make any API calls that you will be needing and then make the javascript plugin match the objective-C function.
*Where you had any calls in your previous views, make those now call the cordova (PhoneGap) plugin.
This is a very brief roadmap to get started.
Once the tediousness is over it is worth it though. I moved my IOS application to Android and they transfer pretty easy.
Cheers