Gryff, no matter how many times you try it, a successful completion of Phase 1 will get rid of your cravings and detox you from sugar. You may only need 3-5 days to do this.
What does change over time is that you lose less and less weight from doing it. The big loss at the beginning is usually due to having a lot of weight to lose and from your eating habits before you started. If you've been on SBD for a while, doing P1 isn't as drastic a difference as it was if you had been eating 18-25 servings of carbs a day, like I was.

Does that make sense?
If you really are having a terrible time of it, try doing just one week of P1...pay attention to your body and when you are no longer craving (at least 3 full days of P1), try moving to P2, SLOWLY, okay? One new thing each week, and change it if it's not working for you.
Hope this helps, hon!