The best answer is:
"In as few words as possible"
Summarizing your main idea is not about covering every detail, and you really don't every want to use as many phrases as possible when doing anything. Summarizing the main idea is about covering the most important concepts of your goal as concisely, or in as few words, as you can. Whether or not you use notes depends on whether notes are permitted, but generally you should use them if you can.