@MattS ,
If you are an admin of the account you would be able to change the outbound caller ID per users/Common Area phones. You will got to Admin > Phone System Manager > Users&Room > pick the user you would like to change the outbound caller ID. >Profile > scroll down to Outbound caller ID and click the drop down to pick your main number if in case that is what you'd like to choose.

If you are a user, you would go to Personal > Phone > Settings > Outbound Caller ID > Click the drop down to pick your desired outbound caller ID.
If in case you would like to change the outbound caller ID in bulk, you can also do it by exporting the current Zoom Phone setup and then re-importing he CSV template that has the updated caller IDs.
Have any of these answered your question? If so, don’t forget to mark the reply as an accepted solution.