Date Picker for iPhone Web Application
The easiest way (and arguably the best way) is to use safari's built in datepicker for your input box using HTML5 type="date"
<input type="date" />
There is an iPhone native style date picker that runs in the browser - http://cubiq.org/spinning-wheel-on-webkit-for-iphone-ipod-touch/11
I know it's an old post, but for future viewers: If you are using jQuery, you can try Mobiscroll, a customizable datepicker optimized for touch devices. It ships whith iOS and android skin as well.
You can't. The date picker is a native control and is not available in Mobile Safari.