Please explain what you are trying to do. By default, a call from an external number, forwarded to an external number, preserves the caller ID of the original caller. No custom dial plan is needed.
If that’s not working properly on your system (you’re seeing the company number instead), this might be forced by the Outbound Route or the Trunk settings. It’s possible that your trunking provider doesn’t permit you to send a number that’s not yours, or requires a special agreement to enable that feature.
Other common sources of this trouble are sending the caller ID in the wrong header or the wrong format (compared to what the provider expects), or failing to include a Diversion or other special header that the provider requires.