I would say it's an okay move for Philly, not good, not bad. He's clearly declining. His numbers last year were pretty disappointing to me considering that by and large he was protected in a platoon and didn't face lefties. He is a solid defensive player.
I love Geoff Jenkins the person, he was a hustler who went all-out and gave his all to Milwaukee for 10 years (a rarity). Once upon a time he was a heck of a hitter too. For his sake (and for me, a Jenkins fan), I hope he rebounds in a park that should be friendly to him.
I fear that the Philly fans will be harsh on him -- he's a notoriously streaky player who's severe uppercut swing can look absolutely pathetic for stretches of time (and ridiculously good for other stretches). That ballpark should suit him though. Overall, I suppose Philly could do worse.