It sounds like PhoneGap is your best option here. Right now, it's the best way to deploy an HTML-based application on Windows Phone. The main thing that PhoneGap gives you is a bridge to the phone's hardware (things like volume buttons, vibration, etc.). It also gives you an easy way to wrap up your application into a package that can be installed like a real native app.
By themselves, other frameworks like jQuery Mobile, Sencha Touch and Kendo UI don't provide hardware access or the ability to deploy the app natively. They are purely UI frameworks, meaning they provide the interface widgets you'll use to build your app but little else. Generally, with these frameworks, you need to host the app somewhere like a website and access it through the browser.
Assuming you're running a Windows machine, you could host the app locally for development using Internet Information Services (IIS). Here's a guide to setting up a site. Then you could open the emulator and go to http://localhost to interact with your app. That would work, but it would be clunky.
The ideal scenario is to use both jQuery Mobile (or another UI framework) and PhoneGap to create a nice-looking, natively installable app.
What I'd recommend is trying to get PhoneGap set up in a VB project. From what I've seen, this shouldn't be too difficult. There are probably some details to work out, but mainly it looks like you need to copy the www and GapLib folders over. Then right click on References and browse to the GapLib .dll. You'll also need to get the MainPage.xaml and MainPage.vb files set up, but they probably just host a web browser control, so this should be straightforward.
Migrating the pieces into a new project should work a lot better than trying to convert an existing project.
If you post specific issues that you run into during the setup, I'm sure you could get them answered quickly.
