There is a field in the gateway configuration where you can define the Calling Party Selection:

The following options specify which directory number is sent:

Originator--send the directory number of the calling device.

First Redirect Number--send the directory number of the redirecting device.

Last Redirect Number--send the directory number of the last device to redirect the call.

In order to select "Calling Party Selection"

Go to "Device >> Gateway"

Select the gateway that you are using

Look for Calling Party Selection

Select Originator

Click Update.