You can't benefit from the spell Astral Projection without a physical body
The term ''physical body'' is used 5 times in the description
By freeing your spirit from your physical body, this spell allows you to project an astral body onto another plane altogether.
Since you don't have a physical body, this spell cannot be used on you.
We could argue that you only need ''freeing of your spirit from your physical body'' for it to work.
But this part makes it clear for me that it can't work:
While you are on the Astral Plane, your astral body is connected at all times to your physical body by a silvery cord.
The silvery cord needs to be attached to a physical body.
(...)At the end of the procedure, her body disappears — dematerialized and absorbed into the psicrystal (...)
Perhaps the silvery cord could be attached to the psicrystal instead maybe since your body is supposed to be in it.
There are probably some ways for you to borrow/have a physical body if you really need one to use Astral projection if the DM rules out the silvery cord being attached to the psicristal. (it could be another question on its own).
This Question:Must the body remain on the Material Plane during astral projection?
Might give you some other details.
I'm copying a part of @Hey I Can Chan's comment because I believe his opinion was very useful.
The majority of rules are written assuming that all
creatures—especially PCs—are corporeal, air-breathing, food-eating,
diurnal, I-only-have-2-hands humanoids. If a creature isn't, the GM
must occasionally adjust the rules to accommodate that "nonstandard"
creature. That's why I totally agree that a high-level ghost wizard
should technically see its astral projection spells fail, but also why
an individual GM may rule that it doesn't.