We had to resist very strongly the urge for Sally to say that Otoh Gunga was full of ponies. At some point in this wonderful fantasy world Sally is building, the GM has to step in with something that requires more response than the players just marvelling at stuff.
"Phanastacorians" is the sort of silly name GMs come up with when pressured to invent something on the spot. The reason we know this is just such a name is that we were discussing this script and realised we needed one, so we put someone on the spot by saying, "Okay, think of a name! Now!" Said person blurted out, "Phanastacorians!" immediately. We knew we had to use it.
Of course, "Gungans" also sounds pretty much like just such a word too.
Qui-Gon: Tell us about this underwater city, Jar Jar.
Jar Jar: Ooh, it'sa made of big balls of glass, all full of air. With lots of fairy lights everywhere. It'sa called Otoh Gunga!
Obi-Wan: Sounds nice. How do we get in? An airlock?
Jar Jar: There'sa magic curtain where we walk inside.
Obi-Wan: Whoa, neato!
Qui-Gon: And what do we see inside?
GM: You see—
Jar Jar: All the peoples are happy to see mesa!
GM: They're not people, they're creatures like you.
Qui-Gon: What's this race called?
GM: Um... they're called... Phanastacorians.
Jar Jar: Gungans!
Qui-Gon: Will these Gungans help us?
Jar Jar: Ooh, yessy—
GM: No, they will not. A guard approaches to arrest you.
Jar Jar: Hey! You're spoiling my game!