https://www.cnet.com/news/android-phones-can-be-security-keys-now/

Convenience is a big hurdle, and Google is hoping to solve that by making your phone the security key. It'll have the same functionalities as a physical security key but won't require you to carry an extra device to keep your accounts safe.

That means that like a security key, your phone will warn you if an imposter website is trying to steal your password. Unlike using SMS or authenticator codes for logging in, security keys have to verify that the website you're logging in on is legitimate.