Phantom Emitters spawn phantoms. When spawned, phantoms will choose a random player unit or structure, travel to it in a straight line, and detonate into a ball of creeper on impact. Phantoms can be shot down using a Coilship.
When a Phantom Emitter is about to fire, an incoming alert is placed in the top left corner of the UI:

Help Tab transcript
Help Tab transcript
The Phantom Emitter produces phantoms. Phantoms are trans-dimensional entities that traverse terrain directly to their targets. Ships can eliminate phantoms. The phantom emitter can also be nullified.
Unit JSON
Unit JSON
{ "type": "unit", "enemy": true, "displayname": "Phantom Emitter", "image": "body.png", "sortingorder": 2, "position": [ 0, 0 ], "pivot": [ 0.5, 0.5 ], "isbuilt": true, "hasphysics": true, "creeperdamages": false, "deadfraction": 0.25, "nullifiable": true, "playercandestroy": false, "playercontrolbuildsupply": false, "playercontrolammosupply": false, "controllers": [ { "name": "phantomemitter", "creeper": 2000 }, { "name": "ondestroy_sandexplosion", "amt": 256, "minvelocity": 1.5, "maxvelocity": 3, "color0": [ 0.2, 0.4, 2 ], "color1": [ 0.2, 0.6, 2 ], "sandtype": 2 } ] }
| Ships |  Apex Ship •  Coilship •  Cryon •  Defender •  Digger •  Duster •  Frigate •  Gunship •  Maker •  Part Ship •  Spirit Ship | 
| Other Player Units |  CBomb •  Dark Echo •  Darkling •  Nullifier •  Ore Miner •  Portal •  Reactor | 
| Parts |  Excavation Lathe •  Kelvin Freeze Cannon •  Mark 1 Cannon •  Mercury Rocket Launcher •  Sentinel Cannon | 
| Enemies |  Bot •  Digimaker •  Emitter •  Fixed Emitter •  Part Emitter •  Phantom Emitter •  Rift Inhibitor •  Spawner •  Thrower | 
| Map Elements |  AC Ore Emitter •  B.O.B. •  Hibernation Pod •  IXE Core •  Info Cache •  Tech Module •  T.O.M. •  Upgrade Gem |