The short answer is no. There is no way you can use the UW qbank on your iPhone.
Here is the long answer. The web-based qbanks from Kaplan or UW tend to be more realistic and they offer the same look-and-feel as the real examination. That said, I believe some people, including myself, learn more efficiently from doing questions than reading books. In that case, a second qbank would be useful. There are quite a few good qbanks in the Apple AppStore, they are usually not made by those big name companies (the exception is Kaplan, which does have an iPhone app, more on that later), but they can be very useful. I have two app installed myself, and I can imagine preparing for the board without them. Being able to study any where I go and at any time really help improve my efficiency.
The first app that I got is the Kaplan, just because it's free. It only has 100 questions, but it's still pretty nice. And if you do have the regular Kaplan Qbank, this will give you a taste of the Kaplan questions.
The second app I got is called USMLExchange, and I am very happy with it. This is THE most useful app on my iPhone now. It is reasonably priced, the question bank is huge, and the questions are quite well written. There are a few other Qbanks in the AppStore, like Exam Master and USMLE iBank, but those are either too expensive or too poorly made.
The bottom line is, you can't use any of your regular qbank on the iPhone until Apple decides to give us the Flash Player, but there are many great alternatives in the AppStore.