On Android, you typically have USB host (at least on any phone that someone interested in this tech would buy). On iOS it's moot since NFC is gimped and can't be used by apps.
Most people don't carry the necessary cable around with them, though. NFC doesn't require any additional hardware.
I use it for generating 2FA codes, Yubico Authenticator works like Google Authenticator except that it requires touching the YubiKey to the phone before it shows the 2FA codes. The codes are computed on the YubiKey: https://github.com/Yubico/yubioath-android/blob/63387c02a39b...
I use it for generating 2FA codes, Yubico Authenticator works like Google Authenticator except that it requires touching the YubiKey to the phone before it shows the 2FA codes. The codes are computed on the YubiKey: https://github.com/Yubico/yubioath-android/blob/63387c02a39b...