When was the last time you saw a competent Shadow DPS repeatedly (let alone even use) use Phase walk in combat during an Op?
Was the downtime required for positioning and casting worth it, did it carry a worthwhile benefit?
Now ask yourself how many times do you see Twin Saber Throw, Electro Net, Saber Reflect, Roll, etc get used in combat in an Op? (from competent players)
Was the use of that ability detrimental to their contribution/job?
The answer to the above should be all the info you need to realize that this ability for DPS is utter garbage in PVE content for consistent usage.
It's just further evidence of the lack of any play-testing done with Shadows in the PVE environment. We get skills that are worthless and detrimental to try and actually use, we get abilities that can get you killed in a boss fight or reset the whole damn fight, and not using said ability hampers your already struggling DPS. We rely on position to enemy to use one of our strongest attacks yet boss fights introduce repeating phases where we cant use that attack and lose DPS, which can lead to death or just simply not meeting the required DPS check to be suitable for the Op difficulty. Until they actually start testing the AC in content we are going to get burdened with sub-optimal skill/abilities and "adjusted" based on the whims of PVP.