If no enemies are nearby, the skill fails and goes on a half-second cooldown.
If the teleport completes, the targeted enemy is inflicted with a status effect causing it to take a scaling amount of extra damage on the next hit, and the skill goes on its normal cooldown.
Upon teleporting, the enemy is rooted in place and cannot turn around.
Pairs well with the Assassin's Dagger and the Blowgun as it enables the player to easily deal critical damage.
Notes
Bonus damage from affixes such as "+60% damage on bleeding targets" is calculated when the affected enemy is attacked.
Because of this, the root effect applied by Phaser is able to trigger the affix "+75% damage to rooted targets", effectively giving the item a +75% damage buff.
The debuff applied by Phaser is recognized as a melee attack and will therefore trigger relevant effects from mutations like Open Wounds and Ripper.
The root effect applied by Phaser can trigger the mutation Heart of Ice, instantly resetting the skill's cooldown.
Due to how the game qualifies what counts as a ranged kill, killing an enemy using Phaser immediately followed by a ranged weapon will not activate the mutation Hunter's Instinct. However, it will activate the mutations Predator and Killer Instinct. Other ranged and melee mutations will work normally.
Trivia
Phaser was the name for the Runner enemy prior to an update. The skill also mimics their teleportation ability.
Prior to v1.4, Phaser had a bug where it caused the Thorny to damage the player when used, even though the player didn't melee the Thorny.
After the Swarm rework in v2.1, Phaser now has the shortest cooldown of all skills.