Trying to be objective, I'm not sure that the Phillies are underperforming much compared to expectations, especially considering the key injuries (Hoskins, Ranger, Harper, and now Alvarado). Sure, some individuals are underperforming (most notably Turner and Schwarber), but others are exceeding expectations (Marsh, Stott, maybe Castellanos depending on how much of a bounce back was reasonable to assume). J.T. is a bit down from last year, but he's on a 4 to 5 WAR pace, which was a reasonable expectation (he was at 6.5 last year).
It's interesting to note that the batters' WAR from baseball-reference was 20.8 in 2022 and is 5.8 so far in 2023, which projects to about 20. The small difference is basically Hoskins' absence.
That means the pitching is what's underperforming this year. I didn't think it was realistic to expect both Nola and Wheeler to match last year, and that's part of the decline. Obviously, Ranger's injury and lack or performance to date is a major factor, as is Falter's decline. Seranthony has really dropped off, too. Kimbrel and Soto have been very inconsistent, but Alvarado, Brogdon, and Vazquez have been good. There are of course the cannon fodder types (Moore, Marte, Uelmen, etc.), but they had those last year, too (Coonrod, Norwood, and Familia, who pitched a lot before they cut him).
The Phillies won 87 games in 2022; at that pace they would have 25 this year, and they have 22. Not a huge drop off. And of course this time last year they were not on an 87 win pace.