From Jon Heyman:

I could be wrong, but I think Greg was actually the longest-running sports PR person in the entire city (edit: I’m wrong; Zack Hill over at the Flyers has that distinction, he’s been with them for more than 25 years). Greg joined the Phillies in 1999 after graduating from Rowan and worked his way up to Director of Baseball Communications. My only interaction with Casterioto was in the summer of 2015, when he threatened to kick me out of the locker room.

Why was he let go? No clue. We have sent out text messages and DMs. We are “efforting more information” on that. I suspect the knee-jerk reaction from fans will be something like “they are paying Bryce Harper three-hundred million but getting rid of the PR guy?” That’s what people said when the Sixers axed their equipment manager a while back. There’s always more to the story, but moves like this generally go down as losses in the optics department, regardless, because it gives off the vibe that these rich teams are penny pinching.

Edit –

Seems like the rest of the Phillies’ PR staff remains intact. They had three people working under Casterioto in the “Baseball communications” department, and then Bonnie Clark sort of runs the show from a macro level. She’s the VP of Communications.

Also, and I’m not saying that it’s the case here, but a lot of times when new GMs and coaches come in, they tend to install their own people. That’s why the Sixers’ equipment guy was let go. Daryl Morey and Doc Rivers kind of just want to mold the staff the way they see fit. These types of things happen somewhat frequently in sports, so I guess it is what it is.