There are some party outfits in the East that have been mentioned or reviewed on here...Cambridge Parties, Norwich Sex Parties, the Greedy Girls Party in Beds...all once or twice a month.
But with 17 parties a week, almost 900 per year, Phoenix probably holds more parties than all the other providers in the country put together, so there's bound to be a time when most can attend. There's a good variety of hostesses that are rotated in different combinations. The ratio is always 2:1 or below, so it offers good VFM compared to similarly low ratio parties in the East.