The Exo Stranger is thrilled. Not only did you accept the power of Stasis, you put it to use by taking down Phylaks and retrieving her Splinter of Darkness.
Continue working with Variks to track down the next member of Eramis's dark council. Once you get a hold of their Splinter, the Exo Stranger can use it to enhance your own, which will in turn strengthen your proficiency with Stasis.
But don't get carried away. You have a way go before you can face Eramis. Now that you've accepted Stasis, you must learn to resist the temptations of the Darkness and use it solely for the good of humanity.
With that, she hands you back your Splinter, now infused with Phylaks's, readying you for the next stage of Stasis.
Attune your enhanced Splinter of Darkness at the Ziggurat in Beyond.