In the Pistol Instructor class I took, most of it involves teaching Phase 2, so basically, you're taking Phase 2 as part of the Pistol Instructor class.
I found the Pistol Instructor class a mere 2 weeks before the class dates, so I basically had 2 weeks to get the class material, blaze through the Phase 1 Online portion and study up on the material, so I could demonstrate the ability to teach.
Fortunately, the Phase 2 exam, as well as the Instructor exam was Open Book. Like many Instructor courses, they don't expect a New Instructor to know everything, as much as wanting you to show that you know where to find the correct answers.
Hope this helped.