Pharl was responsible for convincing Vic Fuckler to join him in overseeing the construction of Echo Base on Hoth. He was kept on as second-in-command under Carlist Rieekan. Rieekan encouraged Pharl to really go for it with his Echo Base designs, and fill that cave up with cool stuff. Pharl spent months coming up with neat concepts, and then getting to see them realized physically by the Rebel construction force. It was truly something to behold, but before the base was even close to complete, the Empire found them.
When all was said and done after the Battle Of Hoth, Rieekan admitted he'd asked McQuarrie to design the base knowing it would soon have to be evacuated. He'd set Pharl up to fail, needing someone with overwhelming artistic energy that would waste a lot of time on nonsense so that Carlist could put together one of his beloved escape plans rather than having an impenetrable base they could easily defend for the foreseeable future.
McQuarrie's outrage drove him to quit the Rebellion and sign up for the Empire, eventually being assigned to Tempest Force. This was The Emperor's best Legion, and was stationed at the Shield Generator on Endor. Pharl was at the front door, which was heavily guarded and saw no action. He was killed when Han Solo blew the bunker up during the Battle Of Endor.