When windows phone users could use their email to log in to game so they can keep their account whatever they change mobile or formatting their devices?!
Actually, the game uses a cloud drive attached to the email address you use to log in to the phone during initial setup. If you change devices, login with this same account. Royal Revolt will ask you if you would like to recover your data from the cloud. You have to install the game, go through the tutorial, and then you prompted with recovery options. Just name your king some other name as your previous name will be taken until you make it through the tutorial.