Meaning of the expression-"You got me"

I was watching "Friends" the other day when this conversation popped up. I am a little bit confused with this expression-"You got me." What does it mean?

What does the speaker intend to say?

Phoebe : I can’t believe you--did this. So, what’s the deal with uh you and Joey?

Ursula : Oh, right. He is so great. But that’s over.

Phoebe : Does he know?

Ursula : Who?

Phoebe : Joey. You know, um, he’s really nutsy about you.

Ursula : He is? Why?

Phoebe : You got me.

I use this expression to say "I don't really know." Phoebe wants to say "I don't know why he's nutsy about you. You got me."

beware: in this instance "you got me" does not mean "you know what I mean".

Here it is a jocular way to say "I don't know the answer to that" -- as in: "you caught me out in a puzzle / riddle / contest of intellectual wit, by asking me a really difficult question."

The subtext here is that Phoebe is telling Ursula that she has no idea why Joey should find her attractive. It's Phoebe being catty.