On this page of the Overwatch 2 guide, you can read about the correct way to verify your account via phone and SMS. You will also learn what it is needed for and it involves.
Why is verification needed?
This process is required, especially for new players. Blizzard explains this, among other things, by the desire to limit the toxicity and the large number of cheaters who cheat in the game.
From the very beginning, when logging into the game, you will be asked to log into your Battle.net account and enter your phone number.
How to do that?
After starting the game, before logging into the server, you will be asked (if you are a new player) for SMS verification. During it, you will need to enter your date of birth followed by your telephone number. After a while, you will receive an SMS with a code that you must enter in the new window to complete this process.