I really need to know, who are you?

My mom got sick. Her throat was really bothering her, and when we spoke Sunday night, I could barely recognize her voice. Mom didn't get better over night, and on Monday, she called her boss, and gave the (extremely unusual for her) "I am not coming in today" shpiel. After explaining for a few minutes why she was not coming in, mom was ready to hang up the phone, when the supervisor asked her, "Guillermo, is that you?"