Just as the graphic interface you use with your own HTML+CSS or Canvas.You can also use ready library, for example JQuery Mobile. Most control elements, such as: Input Fields, Navigation Bar, Drop Down Field, Checkbox etc., are realized in JQuery Mobile. Furthermore, you can choose your color scale and design, plus the visual interface construction, with Codiqa.
PhoneGap allows you make cross-domain Ajax requests to connect you with your server or you can use for it WebSockets. The biggest advantage of this approach is to create Mobile Apps and when written once, this code will work on all popular platforms. A significant advantage is also that the web developer can quickly develop programs for mobile devices while not wasting time on learning new technologies.
See also: jQuery optimization on the site (Part 2)