To help decide whether your UI should be a page, consider the following questions:
Would the user explicitly want to visit the page?
Would the user remember being on this page and want to return to it?
Pages hold discrete sections of content in apps and appear as separate screens to the user. You can create as many different pages as needed and construct their UIs to present content within an app and then provide navigation to those pages from the frame or page if you like. Simple apps may require only one page, while more complex apps may require many pages.
Full-screen view
You can also implement a full-screen view where the Status bar or App bar can optionally be displayed, but this must be explicitly defined using the visibility property, because the default is to not display them. The best practice for a full-screen view is to not display either so that users can focus on the content experience. Notifications and incoming calls are still displayed in full-screen mode, even if the Status bar or the App bar (or both) is hidden. For more info about the Status bar and App bar, see Essential graphics, visual indicators, and notifications for Windows Phone.