I'm sorry this happened. I know how it feels. Usually, when I start stuttering, I will immediately stop and call attention to it. I shouldn't apologize for having a stutter, but I do. I will say something like, "Sorry, I have a stutter. Certain words take me a bit longer." 9 times out of 10, I will get a smile and a "Omg, don't worry about it! Take your time." In this situation, if I didn't bring attention to it, I would definitely email them - but not about the stutter. It's good practice to email and thank them for their time and confirm you want to work there. I would say, "Good morning, \_\_\_\_\_\_\_. I want to thank you for speaking with me today. I am excited about the position and look forward to speaking with you again. I also wanted to thank you for your patience. While I don't allow my stutter to hold me back in life, it always seems worse the phone. If I can provide clarity about anything we discussed, please do not hesitate to contact me. Sincerely yours, Teem47."