Hide CallerID for Internal Calls

Does anyone know how to hide the callerID for internal calls? Using FreePBX v2.11.3

I did locate this document below but could not follow this. If anyone can better explain or know if this would work. So to be clear, the PBX is for internal calls only, no external connections to any PSTN. Don’t ask me why, but we need to block the caller ID of all calls and they are only internal.