With the coming Windows Phone 8.1 major update – already available for the developers but you can even get it by register yoursef for free and get the Preview Developer Windows Phone app, a major and missing feature is now available; Project the Windows Phone screen on your PC.
You must have the Windows Phone 8.1 update installed on your mobile device and the Windows application available here http://download.microsoft.com/download/A/2/7/A271EFFF-6C9E-4E9B-9259-0F72FDEDD153/ProjectMyScreenApp.msi
After installing the client application, go the System Settings on your Windows Phone to reach the Project my screen section – your device MUST be connected to your client using USB
Once you have installed the Project My Screen application on your client, launch the app and connect your Windows Phone using USB.
You will be asked on your device to allow the projection and then it will display your Windows Phone screen
By default, the application is starting full screen; to switch to windowed screen, just use the Alt+Enter keyboard shortcut (it will also get back to full screen)