"Physical spells only affect the physical realm." (p131)
"A manifesting
astral projection has no physical presence,
meaning they cannot interact with the
physical world, and they are not captured on
any recording equipment. You also cannot
cast spells at targets solely on the physical
plane, but you can communicate with the
people in the vicinity as if you were there." (p160)
Given how even Manifesting won't let you cast spells aimed the physical world/realm, and Physical spells cannot be cast outside the physical world/realm, in astral you cannot cast at all. And Manifesting Spirits cannot be buffed by Physical spells.
Materialization, however:
"This power allows astral beings to take shape in
the physical world and form a temporary “body”
to inhabit while they’re here. This lets them interact
with, and affect, physical beings."
So yes, you can Heal a spirit.