This trophy unlocks from using constructs to kill 100 enemies. Constructs are considered to be your Turret and the Remnant VI.
You can unlock your Turret right away in your skill tree. The Remnant VI does not unlock until you have done PeeBee's first side mission.
I did this entirely with the Turret and also made sure that my Turret was maxed out to Level 6. The Level 6 upgrade to add the Flamethrower, does a tremendous amount of damage to enemies and is highly recommended.
Kill 100 enemies with either the Turret or VI to unlock this.