Is it mandatory to use Two-factor authentication to access myPhonak account? 

Two-factor authentication (Multifactor Authentication) is not mandatory, but it is recommended as it adds an extra level of security to your account.  

Two-factor authentication is disabled by default and can be enabled by the users if they wish to. It can be managed in the Profile->Personal details section of myPhonak app.   

Two-factor authentication works only when the user has an account with a set password.