Prerequisite: Priority: The Citadel II
Overhear the angry elcor just outside the Purgatory elevator on the Citadel.
Walkthrough EditPhontes system in the Silean Nebula. Return it to the elcor just outside the elevator to Purgatory on the Citadel.
Note: the Phontes system will be accessible after you complete the Priority: Rannoch mission.