Variks is surprised and impressed that you managed to defeat Phylaks. He now believes you may be capable of wielding Stasis without being corrupted.
He tells you that your next target is Praksis, the Eliksni who created the technology that allows House Salvation to wield Darkness. Defeat him and Eramis's plans will come to a halt. Variks believes he's been experimenting on the Vex, and if you disrupt his experiments, you might get his attention.
Investigate Praksis, the Technocrat's plans in Asterion Abyss.