Hie… I am developing a game… The Android Build for the project is 13mb… but the Windows phone build for the same project is 402mb… I really have no idea what could be the reason… Can anyone give me some suggestions?
Well in the comments you said that the project exported by Unity is 400+mb.
It’s totally normal, as Unity exports a SOLUTION for visual studio and not a ready to play binary file (as it does for Android)… it’s a big directory full of stuff. But don’t worry.
You just have to open the .sln file with Visual Studio (2012), configure the MainPage.xaml if needed, connect your Windows Phone to your computer, choose “Device” on the right of the small green arrow in the toolbar, and click on this arrow (don’t forget to unlock the lockscreen of your phone first).
“Et voila”.
Your game should now run on your phone, then you’ll be able to test it and debug it.
Once you made that, you’ll find a XAP file in the directory “YOURPROJECT/Bin/ARM/”. This XAP is the APK of Windows Phone, the binary. It should be way lighter than 400mb 
Once you will want to put your game on the store, you’ll just have to send this XAP file.
I hope it helped.
Cheers.