I'm looking at some flights EWR-PHX on united.com, there is a cheap first class ticket EWR-DEN-PHX available in P class. UA P class is sold as first on united.com, but it's listed as business class in the mileage accural tables of AC Aeroplan, A3 Miles and Bonus, and OZ Asiana club.

What's the deal with P class? Is it business or first? If it's first, then why is everyone else calling it business? If it's business, then why is UA selling it as first?