The Phone Callback method is one of 7 available authentication options when authentication is requested. When authentication via phone call is requested, you will receive a phone call instantly to your enrolled device. After answering the call, you will have the option to either accept the authentication by pressing "1" on your keypad or the option to decline the authentication by pressing "0." You can use this method with any landline or any phone you have enrolled into your Duo account. If the authentication fails, you may select the option again to receive another callback or utilize another option.