Have you ever thought about bringing up the fact that you have a stutter at the beginning of the interview? Getting it out in the open at the start might be better than apologizing at the end. I'm glad you took positives from the experience. Over the phone it can be extra hard for us since the person might not recognize the fact that we have a stutter, especially if we're trying to hide it. So they might be thinking we are answering strangely or are unprofessional unaware that there is a different reason. This is where advertising in the beginning can help and put you both at ease. I only had one unexpected phone interview but it worked out really well for me. I was actually still asleep when I got the call and I was about to ignore the call when I thought, maybe it's an interview call. I answered and it turned out to be the CFO calling about a position I applied for and asked if I had 5 minutes for an interview. I said yes and luckily I was still in sort of a sleepy daze because I was too sleepy to worry about my speech but aware enough to answer professionally. I got the job so that was a good experience for me.