The problem is two-fold: the Phillies have been unable to draft & develop viable alternatives and, because they pay these guys so much and have a bloated payroll otherwise, they cannot afford to sign viable alternatives either.
Until the farm system can actually produce a viable OF or C starter for the big club, that avenue is closed. And until they free up payroll and roster spots, it is going to tough to sign viable options for RF or C in FA and/or trades.
They are stuck doing what they have done, bringing in players without many options due to significant flaws and/or less talent and hoping that someone has a career year or their coaches can help them figure some things out.
Now, Realmuto is up and all I hear is that the Phillies need to extend him again. I love JT, but this just screams incompetence IMO by Phillies management. This is JT's 7th season here and we still have no one viable to replace him. At least this is only Casty's 4th season, but the Phillies ineptitude with farm hand OF has a much longer history unfortunately.