[simias]

Security tokens are more secure and can't be as easily fished as phone-based 2FA solutions. It's not about using the key on a mobile phone, it's about replacing phone-based 2FA.

You're right however that their key doesn't seem to have any interface other than USB so it won't be practically usable on smartphones. Yubico has NFC tokens[1] for that use case but it doesn't seem that Google's version offers that yet.

[1] https://www.yubico.com/products/yubikey-for-mobile/

[rlac16]

The page Using Security Key links to mentions that Titan supports Bluetooth & USB, with NFC support in a future update.

https://support.google.com/accounts/answer/6103523