Charge to Bill through the Microsoft Store

Sign into Microsoft Store - www.microsoft.com/store

Select your name in top right of screen and click on My Microsoft Account

Select Payments and Billing from dropdown and select Payment Options

Select Add a payment option

Select Mobile phone

Pick EE as your mobile operator and enter your phone number

You'll then be sent a verification code and be asked to enter it on the next page

Once verified, you'll be able to select your mobile phone number as a payment method when purchasing a game, app or content