Yes, it is. When you update any of your details (for example, your bank details or postal address) you will need to enter a verification code which will be sent to your registered mobile phone number via SMS, in order to complete the update. For convenience, you will only need to do this SMS verification once per login session and only when you wish to make changes to your details. If you are simply logging in to view your investments, you will not need to verify via SMS.
You will also have the option to set up an alternative email address that will allow your to use as a backup where you can also retrieve a verification code in case you do not have access to your mobile phone.