I'll start off by saying I have no idea. Still, just going alphabetically through the roster, we saw Aaron Altherr's bat go from a triple slash of .236/.287/.399 in 2014 to .293/.371/.480 in Double-A in 2015. Maybe that's just an adjustment to level, but, Altherr actually hit better in Triple-A and scouts had some fairly glowing, if hyperbolic, reports on him. More impressively Altherr went from a guy with a fairly high K rate and Low BB rate to a guy with a virtual even split between the two (15.4% and 10.8%, respectively). I'll skip J.P. Crawford, since he's been a good hitter with a good approach all the way up the ladder. Same for Kelly Dugan, though his 2015 in Reading is only rivaled by his 2013 in Clearwater for quality of his line.
There's an additional series of Org. fodder who are suddenly putting up uncharacteristically good lines. Brodie Green is having a career year at the plate with more Walks than K's (albeit with nothing you'd consider Power). Gabriel Lino started the year in Reading and showed a higher BB rate, lower K rate and more power than he has in years (not to mention a better glove, though that's a different article). Harold Martinez spent his previous 3 years in the Org showing the same mix of awfulness and incompetence we've all come to expect from our Second Round picks before suddenly becoming surprisingly solid this summer going .302/.345/.433. I'm hesitant to call him a prospect, but it is the first season in a few years I've bothered looking at his line much. Speaking of guys I've ignored for 4 years, Angelo Mora has gone full beast mode with a .343/.436/.582 line (A 14% BB rate from a guy who usually hovers in the 3-5% range). And, of course, I need to mention Brock Stassi who went from a light hitting First Base player to a suddenly effective hitter (though with far too little power for First). His slash used to average in the .240/.300/.330 range is suddenly .308/.397/.459.
We shouldn't forget the injured Roman Quinn here either. Preseason the Roman Candle was highly regarded for his speed, but the bat was seen as questionable by many analysts. Quinn had previous slashed in the .250/.330/.340 range, but this was while learning to play, arguably, baseball's toughest position and simultaneously learning to switch hit. The bat would clearly take a while... or wouldn't, actually. Quinn put up a .306/.356/.435 line with a nearly 5% drop in his K rate.
Obviously, I have saved the best for last as Andrew Knapp, who I expected to be a kind of Ryan Doumitt Offense First Catcher with suspect glove suddenly morphed into Mike Piazza. Currently everyone agrees this isn't sustainable and we likely don't have the Catching equivalent to Barry Bonds. That said, there is clearly some legitimate improvement. Knapp has been lucky, but he has also been crushing the ball. This may be the first time Knapp has been fully healthy since we drafted him, so maybe we're just now starting to see his real skills.
So, what the h-e-double-hockey-sticks is happening in Reading? Part of it can probably be written off to Reading being an Offense Friendly environment (especially for Homers when the wind is blowing). Some of it could be the odd wave of career years all lining up together. But I see another distinct possibility: The Phillies really have something in Hitting Coach Mickey Morandini. Brock Stassi is having a career year after adding a leg lift to his swing. Andrew Knapp's Right Handed Swing is noticeably different and smoother. Several of the hitters have seen noticeable improvements in approach. It's hard to narrow down, as many of these guys also spent several weeks in Clearwater, so changes may have been begun there and only become apparent in Reading. There are also guys who are floundering or stagnating (hello Pointer and Perkins),but I'm very intrigued in Mickey Morandini, Hitting Coach.