What would happen if someone were to place a Portable Hole within a Bag of Holding while being within the Astral Plane? Would it be the reverse effect?
According to the description it would still create a gate to a random location on the Astral Plane.
Placing a bag of holding inside an extradimensional space [...] instantly destroys both items and opens a gate to the Astral Plane. The gate originates where the one item was placed inside the other. Any creature within 10 feet of the gate is sucked through it to a random location on the Astral Plane. The gate then closes. The gate is one-way only and can't be reopened.
It would be a Gate from one location in the Astral Plane to another.