It's likely used playfully or humorously, and its meaning depends entirely on the context.
Here's why it's probably not a real phrase with a defined origin:
* Sounds nonsensical: The combination of the words "oogley" and "moogley" is nonsensical and doesn't sound like anything with a real meaning.
* Common use in humor: The phrase is often used in a humorous way, implying it's a made-up term.
* Lack of recorded history: You won't find any significant references to "great oogley moogley" in historical records or dictionaries.
So, if you hear someone say "great oogley moogley," it's probably just a bit of lighthearted fun!