This is the basic process for Windows Phone 8, not sure if this applies to Windows 7.8 phones, but it may help to get you started!
Firstly you would need to download and install Visual Studio Express 2012 for Windows Phone
Next export your project from C2 using the option for Windows Phone 8.
Then click the exported solutions file (.sln extn) which will open up in VS 2012. From there you can configure your project and test it on an emulator or a device.
There is also a really useful plugin for Windows Phones (created by thehen) - click here to find out more
Hope that helps :)
Edit: Ashley also created a very good tutorial that you may find helpful (click here)