Hi. I work as a therapy aide in a philly rehab hospital. Most of my observation hours were from up north when I went to school in central jersey.
However, have you thought about obtaining hours outside of the city? I got OT hand therapy hours around Marlton, NJ. They were very accommodating and let me come in whenever I had time!
I would stay away from hospitals because you would have to get a volunteer position and you would have to reach a specific amount of hours in order for the Head Rehab Director to write a rec letter or eval. Also, you may or may not even get to observe that therapist much which makes it harder to form a good relationship with them.