Phantom is a radar jammer ship, allied units nearby vanish from enemy radar. While bereft of armaments the Phantom plays a vital role in keeping your ships from the enemy radar screens. But beware, the Phantom will not stop the enemy spotting your ships visually and line of sight will make the Phantom ineffective.
Combining a cloaked unit with a jammer makes a given unit totally invisible.
Place one amongst a group of missile cruisers. While undetected they can maneuver around the enemy flanks and bring about terrible damage to the foe. Once the attack is complete they can escape out of sight and become difficult to hunt down.