You no longer require Android to use your phone as a Google security key. Google has updated Smart Lock for iOS to enable you to use your device’s “built-in security key” — that’s the Secure Enclave constructed into each iOS device with Touch ID or Face ID. From then on, you will just want your iPhone or iPad nearby (plus your typical password) for two-factor authentication whenever you sign in to Google on desktop utilizing Chrome. It uses a Bluetooth connection to assure that it is actually you and not some distant intruder.
This won’t allow you to authenticate non-Google accounts, after all, and it could be a pain if you’re the kind who upgrades devices frequently. It would beat having to purchase a dedicated Bluetooth key in certain circumstances, though, and it is more secure than relying on SMS-based authentication.