If public speaking scares you so much, then I suppose the best advice would be to avoid it. I am always puzzled when actors admit to extreme stage fright as, to me, it is not an endearing trait. Considering all the unpleasant features that can accompany this level of anxiety, it would be far less stressful if you went and got another job.
But despite having a fear of public speaking, like many things, it’s not too bad once you’ve done it and you may even find it enjoyable. I know from experience that you can gradually build your confidence with nothing more complicated than asking a question at a meeting. Any meeting will do: residents,neighbourhood watch, community association AGM; just ask a question and take no notice if someone says that your point was discussed at a previous meeting – tell them you weren’t there.
Public speaking is a very formal title for what in many cases is no more than “saying a few words”. Slowly building your confidence will make those few words a lot easier.