I think every exchange site warned you properly regarding 2factor authentication, told you the risk if you ever lose your phone and cannot access your account anymore. It is our Job as a user to save what ever code they might told us. If you properly keep safe your code this won't be problem to you. Bittrex is great, very user friendly but Binance has more coin that they support. I think right now Binance is the top exchange site as of the moment.