Definitely sounds like a Voltage Boosting setup here - in the form of an Isolated Transformer, rather than the more commonly used "Brute Force" approach with Autotransformer connected 1 Ø Transformers.
How do you get 208V Delta?
The Primary Windings are connected as a Closed Delta 3 Ø 3 Wire arrangement - as is common with many 3 Phase Low Voltage Dry-Type Transformers.
The Secondaries are connected as a Wye, with provisions to land a Common Conductor to the Star Point via Terminal "X-0"
The Primary Windings of the Transformer mentioned in this thread, are wound for an input Voltage level of 208 VAC nominal, and are simply connected in Parallel to each other - resulting in a Delta configuration.