The main telephone number linked to your account can be connected as an alternate username. You can do this either before or after linking your phone number on the Phone numbers page: simply check use phone number as a username.
Each telephone number can only be used as an alternate username for one account. Likewise, only one alternate username can be connected to an account. Only the main telephone number can be used as this username.
Let's say that you use the number +1 564 1234567 as an alternate username. Now you can:
Enter the telephone number (without a plus sign or spaces, e.g. 15641234567) everywhere you need to enter your Yandex username.
One exception to this rule is on the Restore access page, where you must enter the username you gave when you registered.
Use the address email@example.com as an e-mail alias.
To send an email to this address, you can enter a number in any format (without spaces). Yandex.Mail recognizes both +firstname.lastname@example.org, and email@example.com.
Messages sent to this address will be end up in your Yandex.Mail inbox (if you have one). This (numeric) email address will stop working if you disable your alternate username or un-link that number from your account.
If your number gets transfered to a different person and the new owner enables it as an alternate username, then that (numeric) email address will also transfer to their ownership. This might happen in the following situations:
If you lose your SIM-card with your phone number, you should restore it by visiting one of your mobile operator's locations before the number can be put back in circulation.
If you changed your phone number, delete the link for the old number and link your new number on the Phone numbers page.