A token is a confirmation code, which, depending on the settings of your personal account, Is received via SMS or is generated by a mobile app. It is required when creating a withdrawal request and internal transfer, changing the leverage or password of a real account, and changing data in the profile.
The token is also required to change the used phone number or verification method to the app. Please note that in this case, you get the code in the way you want to replace it. If you try to link your personal account to a new number, the token will be sent to the number you entered during registration.