I know that situation all too well. Since they already know that you stutter. I would call them and just say “I’m sorry, but I just missed a call from the hiring manager. My name is whatever your name is. I usually just say my first name first and then if they ask me my last name I’ll say my whole name. That way my last name just follows after my first name right away. I don’t get stuck if I use that trick. Almost 75% of the time I start with my last name I’ll get stuck on it and it starts with an ‘E’.