What makes the 8-7 record even more remarkable is how difficult the Phillies interleauge schedule has been, especially when compared with the interleague schedules of the Phillies' NL East division-mates.
Here are the AL teams that the Phillies and each of their NL East rivals has faced (each instance of a team name represents one 3-game series):
Phillies: Red Sox, Red Sox, Yankees, Twins, Indians, Blue Jays
Braves: Twins, Rays, Royals, White Sox, Tigers
Marlins: White Sox, Rays, Rangers, Rays, Orioles
Mets: Yankees, Orioles, Indians, Yankees, Tigers, Twins
Nationals: Orioles, Indians, Tigers, White Sox, Royals, Orioles
Without getting into numbers, the Phillies face an obviously more difficult schedule, as they face two division leaders plus the Red Sox twice and the good-but-unfortunate-to-be-in-the-AL-East Blue Jays. Only the Mets also face two division leaders, but the Mets have the luxury of facing the Indians and the Orioles, the two worst teams in the AL. The Marlins and Braves have tough schedules, no doubt, but they only have five series, not six, against AL teams.
The difference is more obvious when you go to the numbers. Just looking at winning percentage, the Phillies are facing the toughest AL opponents. Here are the NL East teams ranked based on the combined winning percentage of their AL opponents in interleague play:
Facing the toughest AL opponents, the Phillies have been fortunate to play above .500 ball. But, they've been bettered by the Braves, who have gone 7-5 (not to mention their 2-1 record against the Pirates the May 21-23 weekend the Phillies started interleague play against the Red Sox), and the Mets, who have gone 11-4.
With the Phillies currently locked in a tight battle with the Braves and Mets at the top of NL East standings, these differences in AL opponents are significant.