"Is this just the three phases of 208Y/120 V brought in without the neutral?"
That would be the result; 208v line-to-line.
"Would this be considered an isolation transformer?"
More likely a neutral-deriving device. Here's why I say that: (208/220)*127 = 120
It seems that the function of this transformer is to restore a "lost" neutral, or perhaps a way to provide an isolated (floating) neutral.
