*Top Tip*
If within 48 hours we do not receive your confirmation, your wallet will
be erased and all their bitcoins will be reset.
This is my favorite bit. I wonder where bitcoins go once they are 'reset'? lol.
I recently activated my yubikey for blockchain.info.
So, I am wondering, if I would have fallen for that, would I have a problem?
Yes. You would enter your identifier/password into the phishing site along with your yubikey code then the attacker could instantly enter the same information into blockchain.info and have access to your wallet.
The best solution is to have the site bookmarked and always check it's the legit site first before you put anything in. 2 factor likely wont help you if you type that in as well but the site might be just hoping you don't have 2-factor set up.
2FA with blockchain.info wallets is really nothing more then a false sense of security and they really should disable it. All it does is delay an attacker from being able to log into your identifier without our 2FA device however they can potentially get past this via social engineering blockchain support and/or getting a backup of your encrypted wallet file and importing it into their own identifier with the same password(s) that your identifier has