Phase Cannon is a new Vasari weapon introduced in Rebellion. It is mounted exclusively on their Titans, the Vorastra and the Kultorask; the former uses four forward-mounted heavy cannons while the latter has a single aft mount.
The fact that all Vasari Titans are ten millenia old may suggest that this weapon is just as ancient, but is somehow limited to the otherwise updated Titan-class warships.
There were no upgrades for it.
While still using the same particle effect, Phase Cannon now counts as Phase Missile weaponry, in addition to Kultorask's front launchers,