It is not mandatory to add your phone number to your account. However, it is needed to use SMS authentication for 2FA. You can add or change your phone number through the following steps:
- In the upper right corner, select 'Personal details'.
- Click on ‘Change number’ in the Phone Number section.
- Fill in your new phone number and your password. Optionally, you must fill in your 2FA.
- Fill in the confirmation code which was sent to your new phone number via SMS.