It looks like Rosetree Park may be just inside of the surface area of Class B airspace for the airport. To fly in this airspace you would need permission from PHL tower, not the rangers. You should be able to obtain this permission if you ask.
I am not sure what you consider the borough, but if you go just a little more to the NW you are out of the Class B surface area. Under Part 107 you would be able to fly in this airspace up to 400'. As an example none of the Springton Reservoir is within the Class B surface area, and I would bet you can get some great flying in around the Reservoir.
A park can make it prohibited to land or take off in the park, but they can not prohibit you from flying above the park in Class G airspace up to 400'. If the rangers are saying it is prohibited to land or take off in the park ask for a copy of the regulations or rules that prohibit this. My guess is they may not actually exist and they may just be assuming it is prohibited. Make them back it up with something.
If you get your remote pilot certificate, this may help you with getting permission to land and takeoff.
