If you first signed up using '44' UK prefix ensure you do the same here. That is replacing the first zero with you country code. So if your UK number is 07885 654321 - enter 447885654321.
If you have already paid for your service from a mobile phone enter that number here. This is the number you used first to sign up for payment of the service.
When you press the continue button you will be taken immediately to the content and be free to browse the complete service. This facility is helpful if you are cut off or disconnected during a session. Even if you have just taken out single day payment you will find this allows you to conveniently rejoin the service during the day.