When you made your last payment, your phone number was saved on file. This feature is similar to a merchant storing your credit or debit card number being saved when you make an online payment, so you do not have to re-enter your account information on subsequent transactions with that merchant.
Phone on File is a one click solution for your mobile payments, which means that once you register, your transactions will be pre-authorized for up to a limit of £100 or 90 days on the merchant for which you opted in to use this service. For subsequent purchases, you will only be charged when you choose to make a purchase and select “buy”.