The purpose of Phase 1 is to eliminate your carb cravings. If that is taken care of, there really isn't a need to go back. A good amount of the weight you lost in P1 was water weight. If you've been following P2 since then, there is a good chance that you won't lose any more weight by going back to P1 than you would by staying in P2.
For heathy weight loss, you shouldn't be losing more than 1-2 lb. a week. 17 lb. is an amazing weight loss, and you should be proud of yourself for that. I think that if there was some magic way to lose more weight faster, we all would be doing it!
Also, keep in mind, with working out for an hour a day, you are building muscle. Muscle weighs more than fat. It will come off, just give it time.
If you are seeing stalls, check your portions. It is recommended that you limit your cheese to 2 oz. per day now. I know that nuts are something that I can easily overeat on, and they are very calorie dense, so make sure you are staying in your nut allowance. Also, check your protein amounts. 3-4 oz. of protein at lunch and dinner is a serving, and though it is technically unlimited, it is something that I try to keep to a serving.
Be prepared for ups and downs. This summer I went almost 5 weeks without seeing the scale move. Plateaus are normal, and sometimes your body needs to adjust. Hope this helps!!