Scientist 36M here (PhD in Experimental Physics, working fulltime at a research institute). I have to give talks pretty frequently, from small in-house seminars to international reserach conferences. Stuttering since childhood, although with advancing my career, my stutter has become less and less. Perhaps it is something that gets better when you grow as a person and have to face different and subsequently larger challenges - at least something that gets better with age (as opposed to back-problems and eyesight ;) ;) ) In my experience, people in the STEM field are pretty chill about stuttering. One of the core advantages of working in science is that most people care more about the content of your talk than how you present it. Also, during my time at university, none of my supervisors or professors ever commented about it. When I activly sought out feedback regarding my stuttering (in university or later in the workplace), I almost always got responses in the spirit of "I have respect and think it's cool that you pursue your chosen career path regardless of your handicap". So to wrap it up: don't worry, you will be fine. The fact that you stutter and decided to enter a PhD program anyway only speaks positively for you. People will recognize that.