It may be coincidental, but my suspicion is that the Phillies have decided to take advantage of a wrinkle in the signing bonus rules - one that some teams have exploited for years, but that the Phils, to my knowledge, have not in the past.
Signed players receive a $2,500 "contingency bonus" that doesn't count against the club's bonus pool. Some clubs have routinely treated that $2,500 as part of the bonus they give the player - and list a bonus, for bonus pool purposes, that is $2,500 lower than what they give the player. Some other clubs don't do this - they just let the player have the additional $2.500.
The thing is, if a club exploits this, they can accumulate (over 20 rounds) an extra $50k in bonus pool money - and that might be enough to make a difference with a tough sign.
The Phils haven't done this in the past, I don't think, although several clubs (Dodgers, Braves come to mind) have.
As I noted, this may just be a coincidence - if we see other guys coming in $2,500 under slot (or something like $52,500 under slot, etc.), that would indicate that the Phils are taking advantage of this rule.