There was a situation that came up at Maryland States this past weekend, and neither myself nor the Head Judge could find an answer among Ashcloud Phoenix's Gatherer rulings nor the Comp. Rules. The situation was:

A player activates Ashiok, Nightmare Weaver's +2, exiling three cards from his opponent's library. One of those cards was an Ashcloud Phoenix. He then asks a judge the following: if he puts the Phoenix onto the field with Ashiok's -X, and it then dies face-up, would it return to the field under its owner's control, or under his control? The ability doesn't specify under whose control the Phoenix returns to the field.

We agreed upon the Phoenix returning under the Ashiok player's control, rather than its owner's. This is different than the reminder text provided for Banisher Priest and Banishing Light, but we felt that the fact that Ashcloud Phoenix instructs the controller of the trigger to return it to the field indicates that it should return under the control of whomever controls its “when ~ dies” trigger.

The ruling you gave is correct; Ashcloud Phoenix returns to the battlefield under the Ashiok player's control. Your logic in doing so is pretty much exactly correct. Unless specified otherwise, permanents are controlled by the player who put them onto the battlefield, and since the Ashiok player controls the trigger, he's the player putting the Phoenix onto the battlefield. The Phoenix's ability doesn't specify otherwise, so it returns under his control.

Banishing Light and other “exile…until” effects are a different situation–they return the permanents they exile to the battlefield under their owner's control because they have a rule that specifically says so. (610.3b)