Phantoms spawn endlessly at night providing easy farming (unsure if that is intended) However, upon killing them, the membranes drop where they die but the experience is ~5 blocks behind that position (it seems to be directional as well, based on player position. Once dead, the phantom is in between the player and experience drop location, though this part is not fully tested)

I would have provided a screenshot if they were easier to take on this platform.