On the Steam desktop app, visit Steam > Settings > Security > Manage Steam Guard. On the web, click your name, then select Account Details > Security & Devices > Get backup codes.

Once done, you should see a recovery code that will help you authenticate your account if you lose access to your phone number. Once you've enabled Steam Guard, restart the Steam app on your PC.

If you think your Steam account is safe, think again—there's word of a massive data breach affecting Steam on the dark web. I'm off to reset my Steam password and enable Steam Guard, just to be ...