Incoming long shitpost:
Phasic seems sort of meh to me with her. Let's look at what you're actually dealing with here:
Centurian, Engineer, Nemesis 2194 shields
Marauder 1974 shields
Cerberus Turret 3038 shields
Atlas 27422 shields
Hunter 2961.5 shields
Rocket Trooper 1755 shields
Pyro 3422 shields
Bomber 1976 shields
Prime 15356 shields
Now that seems like a lot but let's really look at it because this is the only defense in the game where Phasic trumps Warp Rounds. Phasic gets a bonus versus barriers but not as much as warp and especially if the barrier is primed Warp is going to have a significant advantage. Phasic's other advantage is shield regen delay which is a pain in the ass on Platinum.
So we're looking at Arc Pistol damage here since that's the example you gave:
For Phasic III (going with charged damage per shot)
130 damage health, 0 damage to armor, 1303 damage to shields, 1303 damage to barriers
For Warp IV Unprimed Targets
521 damage health, 521 damage to armor, 0 damage to shields, 1042 damage to barriers
For Warp IV Primed Targets
1042 damage health, 1042 damage to armor, 0 damage to shields, 2084 damage to barriers
So you're going to see a significant advantage in TTK against two factions with Warp versus Phasic without any argument, Collectors and Reapers are easily going to be killed faster with Warp Rounds. Cerberus is arguably easier with Warp Rounds as well because Phantoms and Dragoons are dispatched easier with Warp Rounds than Phasic, Centurians I guess would be the only legitimate threat for Cerbs that has shields unless you consider the walking bullet sponge called the Atlas threatening. Geth is about the only enemy type that is arguably better with Phasic and even then you'll dispatch armor much quicker with Warp Rounds. So if playing unknown, unknown or Platinum you're always going to be better with Warp Rounds in TTK. Another factor is shield regen delay which is a huge factor on Platinum but with Dark Channel that is taken off the table as an advantage with Phasic.