This honestly seems like a bad idea if taken exactly as worded.
You hit an enemy with this "phase sinker" and phase them.
They are now invulnerable, but unable to fire weapons.
This means that they will be dissipating flux as if they were not firing weapons, meaning they'll have gained a nice chunk of "free" flux when the phasing ends.
A tweak that could make this actually useful:
An enemy hit by this beam is "frozen" in time, so they can't move / dissipate flux / reload weapons / recharge systems / etc.
This would allow you to use it to knock someone out of the fight, and then:
Safely vent in their face / use it as an opportunity to retreat / flank them.
It would be extremely powerful, and i think would be better suited to be a shipsystem on a specialised ship, rather than a modular weapon.