Ok, let's review:

The 3 *p*_{z} orbitals on the 3 chlorines belong to symmetry groups:

A"_{2} and E"

The *s* orbital on the central P atom belongs to symmetry group A'_{1}.

The *p*_{x}, *p*_{y}, and *p*_{z} orbitals on the central P atom belong to E" for *p*_{x},*p*_{y} and A"_{2} for p_{z}.

The *d*_{x2-y2} and *d*_{xy} orbitals on the central P atom transform together as E'. The *d*_{z2} orbital transforms as A'_{1}. And the *d*_{xz} and *d*_{yz} orbitals transform together as E".

So, look for matches.

A"_{2} of the 3 chlorine *p*_{z} orbitals matches with the *p*_{z} orbital on the central P atom.

E" of the 3 chlorine *p*_{z} orbitals matches with the (*d*_{xz},*d*_{yz}) transform. So your answer is the *p*_{z} and *d*_{xy},*d*_{yz} atomic orbitals on the central P atom.

Now, if you think about the fact that in order to interact, orbitals have to be aligned correctly, this makes sense. Obviously the *p*_{z} orbital on the central atom should be able to act with the *p*_{z} orbitals on the chlorines. The doubly degenerate representations are a little harder to picture, but again if you consider the way that the *d*_{xz} and *d*_{yz} orbitals on the central atom are aligned, you should be able to visualize how they might interact with the *p*_{z} orbitals on the chlorines. Compare that to, for example, the *d*_{xy} orbital, which is in the molecular plane - there's no way it can realistically interact with the 3 *p*_{z} chlorine orbitals.