Old leaves. Needs a little more light. Water a little more. Feed weakly/weekly. Lots of subtle reasons. Usually a little more light and water will do it. But not always with leaves that are already hanging. This was in sad shape when I got it. All the leaves were drooping badly and the lower were wrinkled. But the new leaves are once again standing upright like they should be. Don't worry about it.
If your phal leaves are floppy, they will never recover and remain in their floppy state. It usually points to irregular watering.
For the new leaves to be firm, you need to make sure they get sufficient water whenever they need it.