Minecraft wiki entry for Phantom_farming, associated text: You will need to build a trap that when phantoms will spawn, they will come to attack you, but instead fly up into a trap that will kill them. Phantoms are scared of cats, so placing one a few blocks under the trap will make them fly up into a trap. You can trap them using boats or minecarts if you are paranoid of them attacking you. You can then kill them however you want, using a sword strong enough to one hit them, using an observer connected to dispensers which will dispense lava for one second (which is enough to take them down to a one hit with an iron sword or higher). It is recommended you also use Looting 3 since that will give you more phantom membranes from the farm.