iPhones running iOS 10 or later can now be used as security keys to protect Google accounts against phishing attacks. Google effectively brought the strongest phishing-resistant two-factor authentication (2FA) to Google accounts on the iOS platform. This comes after Google also made using the security key built-in Android phones running Android 7.0+ (Nougat) generally available last year, and previously allowing iOS users to verify sign-ins into Google and Google Cloud services with the help of Android phones.
Source: https://www.bleepingcomputer.com/news/security/iphones-can-now-double-as-a-security-key-for-google-accounts/