How do I add a phone number to my Steam account?
To add a phone number to your account or manage a previously added phone number:
Log in to Steam (using the application or a web browser) and click on your account name located in the top right corner.
Select 'Account Details' from the dropdown menu.
Under 'Contact Info', select 'Add a phone number'. If a phone number has already been added to the account, you will see 'Manage your phone number' instead.
Enter your phone number and select 'Next'. We will send an SMS message containing your confirmation code - Enter this code to verify that we have the correct information.
You're done!