If someone overindulge during Phase 3, should they follow the Phase 1 sheet for the next day?

It really depends on the client as well as on the “slip-up”. Overindulging in one meal or with alcohol can be corrected the next day just by returning to their daily macro needs targets. However, certain clients who have a more challenging time recovering from slip-ups (for example, very carb-sensitive clients who experience severe cravings as a result of just one slip up) would benefit by following that slip-up with a Phase 1 day (or two).