Think of it this way. The higher we go, the closer we approach the ground of another planet! So there's really no such thing as 'too high'.

[That was totally reassuring she's sure.]

First stop... Let's see if that invisible barrier or whatever really surrounds the whole city.

[Fwoosh! Phantom Girl's max speed isn't anywhere as impressive as say, Superboy's, but she can manage a steady clip.]

((And I think this is probably a good place to stop! Thanks for indulging me; I'm vaguely tempted to app for real now!))