From the linked article:
"Barajas will be considered insurance for Carlos Ruiz, who will be a 28-year-old rookie next season. Ruiz's injury history and inexperience - he has played in 27 major league games, all last season - made the Phillies leery of entering the season without a proven backup."As you may recall Barajas backed out of a deal with the Jays several weeks ago that would have paid him $5.25 million over two years and Barajas would have been the Jays every day catcher.
So Barajas has one less year guaranteed and isn't assured of a starting spot for the Phillies.