[help] - call divertion

Hello @all,
I have this scenario:

Phone_A is diverted to Phone_B.
Phone_C calls Phone_A and Phone_B rings.

Caller number is Phone_C
Redirect number is Phone_A.
Called number is Phone_B.

The caller number is stored in callerid(num) variable.
How can I get the redirect number? Is it written in some channel variable?

Thank you for the support.