Honestly, just practice. I remember 2 years ago, I had my first phone screening interview and I was so nervous. I stuttered basically the entire time and I was so embarrassed. I could barely say a complete sentence without stuttering. I didn't get the job and I thought at the time, it was because of my stutter. Now looking back, it could've been for a million other reasons. I've had MANY interviews for jobs, volunteering, and school placement since then and now, I stutter a lot less. I think it's kind of like exposure therapy. The more that I talk to new people and do interviews, the less nervous I am and the more fluent my speech sounds. Have you had many interviews in the past? It's normal to be scared and if your stutter is severe, I would just acknowledge during the interview that you have a stutter. Better to be transparent from the beginning.