Building games for Windows Phone 8 is very similar to building games for Windows Store. The process is not identical though. Some of the differences include different Visual Studio project exported by the Editor, scripting based on .NET for Windows Phone instead of .NET for Windows Store and hardware more similar to that of iOS or Android.
Download the Windows Phone SDK 8.0 which includes Microsoft Visual Studio Express 2012 for Windows Phone. If you already have Visual Studio 2012 Professional or higher, the SDK templates and tools are integrated into your existing installation of Visual Studio. Windows Phone SDK 8.0 requires 64-bit Windows 8 Pro or higher. You can’t develop Windows Phone 8 apps on Windows 7, XP, OS X or Linux. Registered Windows Phone 8 device is needed to test your apps. Instructions on phone registration can be found here. Windows Phone Emulator will be supported in future Unity releases.