When registering your Fido My Account, there are two profile types that may apply to you: Account Holder and Subscriber.
An Account Number is required for an Account Holder registration. Those with an Account Holder profile have full access to manage and view their account (view bill details, change plans/contact info and more).
A Subscriber profile only requires a valid mobile phone number and is meant for additional wireless lines on the account (to view usage without ability to make changes to the account).
All Fido postpaid customers who manually self register to My Account on the website have the option of choosing a profile type. An Account Number is required for an Account Holder registration, whereas a Subscriber profile only requires a valid mobile phone number.