I'm in the performing arts by profession and had to work through performance anxiety. I think there can be advantages and disadvantages for the INFP type. The following are a few things that caused my anxiety.
1. The social environment: Being in a highly competitive environment in which both success and failure in performance had negative social consequences of different sorts was one source of anxiety. I would tend to focus on possible social outcomes. Knowing other people to be competitive and primarily desiring their own success results in them often feeling badly if someone else does well. Failure shames mentors and peers who identify with the performer. A performance generates many complex social and emotional outcomes. Because of this environments like church were actually worse than the university and professional settings if I knew there were going to be social consequences I didn't want to deal with.
2. Instinctual awareness: The act of having a group of individuals staring at you while you perform a task has good reason to trigger fight or flight instincts. Staring in nature typically means you are going to be eaten or chased off someone's territory. Staring is equivalent to aggression in nature. For whatever reason human society creates activities in which this is not the case, but there is still an element of judgment that occurs. When you add a dark room, bright spotlight, and loud applause, the instincts can be further triggered.
A couple of things that can help include rigorous preparation of both the materials and the performance/speech. These are two different activities. Performing is a social activity that must be practiced in its own right in order to be prepared. Planning gradual steps between where you are now and where you need to be to give the speech is important. Perform for a friend, then a group, then in the setting in which you will have to give it, etc. If I have an important performance, I find a way to execute it at least 5-10 times in other settings. Nursing homes are great for practicing because they are appreciative and sweet about it in most cases. It also helps to focus on whatever few or many people will get something positive out of it and try to dismiss the negative reactions from the mind. Also, giving oneself permission to fail helps - it's actually okay to be human. I also try to imagine my own reaction if someone else fails. If I know my reaction to be kind and fair, then I know that is possible from others as well. Realize how much will stay the same in you life - the people who love you will still love you, whatever skill you possess is still present inside, etc.