Mass Effect 3.7: "That was for Thane"

[Psyren]

Are you certain that's how Stasis works?

Yes - they describe this behavior right on the wiki:

"Only damage to the health of enemies is considered "damage done" to enemies in Stasis. To prevent unintentional releases of enemies in Stasis, do not inflict any health damage to them as the damage threshold is extremely low. "

It will hold a Phantom - or multiple Phantoms (/Marauders/Centurions/Collector Captains/Hunters etc.) - until barriers/shields have been removed. Getting trapped enemies to one bar of protection before a detonate is the most effective use of the power.