Forward CID to misc destination

sorry if there is answer to this already. I m new to asterisk and FreePBX, so looking for detailed solution.

We got SIP trunk configured, with inbound and outbound routes.
Siemens VoIP phones configured.

When I call our external number it get’s forwarded to VOIP, and CID got displayed, all good.

Sometimes we want to forward calls to another external destination(my mobile), and instead of caller ID, I see SIP trunk number.

Our provider sad that we need to pass code to their server 1
as example add to extensions.conf
exten => _

Can you advice how to configure this in FreePBX ?

thank you.