He's not in.

Hi, everyone.

Business conversation on the phone:

Can I speak with Mr. Cruise?
I'm sorry. He's not in.

He's not in only means He's out of the office?

That doesn't mean He's not at his desk at the moment but he's in somewhere in the office, right?

Thanks.
LiJ

That doesn't mean He's not at his desk at the moment but he's in somewhere in the office, right?

 The usual way to give this meaning would be "He's away from his desk right now."

(Be aware that in the real world, a secretary might be instructed to say "He's not in" if the person is right there but does not want to speak to the caller.)

This is interesting to me.

Let's say the callee says:

He is not here.  => means the callee looked around and he didn't see him there. He could still be in the office but not anywhere visible to the callee.

He just walked away => means he just walked away from his desk. He could be somewhere in the office or out of the office.

He just walked out/ He is not in / He is out => means he is out of the office but he is not on leave.

He has not come in => means he is late for work

He is on leave => means he won't come in at all

Please correct me if I am wrong.

Well, at one time I was "on maternity leave," but I guess you never were, Clive!  You might say someone is "on sick leave" if they are planning to be away for a lengthy illness, perhaps not even receiving any salary, but the company is holding their job available for their return.  Or someone who has been removed from their job pending investigation of possible wrongdoing might be on "administrative leave"  while the company decides if they should be fired or not. (I don't know why it's called that.) But if you just go away for your annual two weeks' vacation, you're on vacation, not on leave.