Some time ago Twitter announced the addition of the two-factor control security feature to each account.
In any account except those of Greece, as the service did not work with Greek phones (++ 30).
From now on, the service is also active in Greece and you can enjoy more security in your account in return for your Twitter number.
You can add your phone number from your account settings, specifically from the following link:
After you add it, you will receive an SMS containing a confirmation number, which you should type in Twitter.
You are ready, as of today you can also enjoy the service.