Two-step authentication in Bitrix24 is set for a specific user's phone (not a number, but the device). So if you've decided to change your phone or have lost it, you'll need to configure two-step authentication again.
How to set up a two-step authentication for a new phone
Open your profile page > click Set up for new telephone. Then configure two-step authentication for a new phone.
User's phone is lost/broken, cannot log in to Bitrix24
If a user has lost or broke his/her phone, an administrator needs to temporarily disable two-step authentication for this user.
After logging in, this user can enable two-step authentication again as described above.
Administrator's phone is lost/broken, cannot log in to Bitrix24
If there are several administrators, this problem can be solved easily. The other administrator should disable two-step authentication for this administrator so that he/she could log in and enable two-step authentication again.
If there is only one administrator, commercial plans subscribers need to submit a ticket to Bitrix24 Support. Free plan users need to contact Bitrix24 Partners first and upgrade to any commercial plan before submitting a ticket to Bitrix24 Support.