Since mail order seats are assigned randomly, accessible seating is not included in the Phish Tickets inventory. Accessible seating can usually be obtained from Ticketmaster, if they are selling tickets for the event in question; when in doubt, please contact the venue directly so they can provide the best accommodation for your needs. If you need special seating please do be sure to obtain this when you initially purchase your tickets, as standard reserved and lawn areas are often not accessible, and in most cases, regular tickets cannot be exchanged for accessible seating after purchase.
When an amphitheatre or arena is built, the parking areas and access roads are designed to accommodate at maximum the number of people that can be admitted to the venue. When people come to a sold-out event without tickets, just to "hang out" or "kibitz," it is possible that the parking areas may fill up before all of the ticketholders have arrived, thus jeopardizing their opportunity to enjoy an event for which they have already paid. In addition, it may overwhelm the access routes, causing traffic jams and delaying ticketholders as well as local (non-concert) traffic.
When people without tickets stay in the parking lots and surrounding neighborhoods during a show, unfortunately it can create tension with the local community (based on prior episodes of inconsiderate behavior, inappropriate urination, or even appropriate urination). It takes only a few local residents left with a bad impression to endanger the band's and the fans' welcome in a town. Therefore, out of consideration for others in the community of Phish fans, please don't go to a sold-out show without tickets - respecting this guideline is the best thing you can do to preserve your opportunity to get tickets and see the band at the same place in the future.