I totally agree. Consider sending and email to the HR contact and explaining that you are interested in the position, explained prior to the interview that you stutter, would like to finish the interview but unfortunately were hung up on by so-and-so and would they kindly reschedule the interview. I am SO sorry this happened to you. Phone interviews are so unfair too! Perhaps suggest a zoom interview too. In my opinion. For stutterers everywhere, you need to politely hold that person accountable. We are here for you. And again I am so truly sorry for the way that asshole treated you!