How to change the orientation of the designer for Windows Phone 8
When you open a Windows Phone project in Design view in Visual Studio, Visual Studio displays a skin that represents a Windows Phone device. You can change the orientation of the skin. The orientation of the skin is preserved when you close and reopen the project.
When you run your app in the emulator, the emulator always starts in portrait mode. For more information, see How to change the orientation in the emulator for Windows Phone 8.
To change the orientation of the designer
In Visual Studio, on the DESIGN menu, click Device Window.
In the Device window, select Landscape or Portrait for the value of Orientation.