Phase Shift is a Ship Achievement for the Stealth Cruiser.
"In the Stealth Cruiser, avoid 9 points of damage during a single cloak."
In the Last Stand, this achievement can easily be earned while fighting the Rebel Flagship's third phase. You will need to cloak the power surge attack at the same time as one of the other weapons. To guarantee it, you can wait for the second time the laser weapon fires, and then use a level 3 cloak. 40% base evasion will give you 100% evasion during cloak.
It is also possible to unlock in an asteroid field, with a long cloak. Asteroid frequency depends on your shields system level, so having fully upgraded shields makes this more likely.
Alternatively you are looking for a ship with Flak Gun II along with another weapon that deals 2 damage.