Nihongo equivalent?
 

there is the english phrase "thats what he/she said!"

is there an equivalent japanese phrase for this?

The closest phrase in meaning and with adequate formality would be:

"Sore o itte itandesu, kare/kanojo wa."

But the native speaker would omit the 'kare/kanojo wa' part almost every time. If the speaker were a young male, you would more likely to hear:

"Sore o ittetan dayo"

The list will go on. It all depends on the gender and age of the speaker, the age of the listener, and what the relationship is between the speaker and the listener.

That's what he/she said!
 

At the risk of piping in where I'm not welcome, there are a few other ways depending on the situation:

...da sou desu (that's what I heard--not exactly the equivalent of he/she said)

For example...

Are they coming today?
Kyou kimasu ka?

They said they can't.
Kyou ha dame da sou desu (they said it's no good today/ can't come today, etc.). More of an emphasis on what you heard vs. what they said, if that makes sense.

Here's another one (a little less formal/ a bit more colloquial):
...da tte

Are they coming today?
Kyou kimasu ka?

They said they can't.
dame da tte (they said it's no good today)

Since you have an exlamation point, I'd go for the da tte or, and you'll get a kick out of this if you're a Naruto fan, "da tte ba!"

...da tte ba! is a little more emphatic ("I'm tellin' ya", etc.) and very informal.

HTH.