We all cave in to weakness once in a while, it's a part of life.
Just give yourself a good shake, take a couple of deep breaths, and climb right back on the wagon again. Each person is different, but I don't think it's neccessary to do a full Phase 1 again. Try maybe 2 or 3 days, and then see how you feel. If you still have cravings, then I'd stay on Phase 1 at least a week.