Phantom has been selling out on some/most nights over the summer as usual, which is typical with or without Norm and Sierra. However, it will not be selling out in September and therefore SRO will not be available. You can do the last row of the balcony for 27 dollars or use one of the many discounts available online.
Phantom is also usually available at TKTS, usually for 50% off. That makes it about $75 for orchestra, not close in price to the last row at $27 but IMHO much better seats and worth the increase.