8% doesn't seem all that big to me, but anecdotally, we've seen the Phillies play better at home (particularly in the season series with the Braves), and then there is a truism that a good team is still only really expected to go .500 on the road, and pile up more wins - and indeed, win almost every series - at home.
There's just so many variables though - the crowd (and the crowd impact on officiating), the comfort of home, batting last, familiarity with the ballpark, constructing a roster for that ballpark (though it doesn't seem like the Phillies really do that per se. Like, on the one hand, ground ball pitchers to try and keep the ball in the park but on the other, bad fielders).