Yes. The procedure to change it is slightly different depending if it is a User Phone or a Room Phone, but in either case, you can choose to use the direct number (for the user or phone), the main office number, or you can block your Caller ID information from being displayed to anyone outside the office.
For a User Phone, the user can configure this by logging in at https://dialpad.com, and click the Caller ID dropdown menu near the top of the page.
For a Room Phone, this can only be changed by an Office Admin. Login at https://dialpad.com, click Office Settings, and click Desk Phones, then Room Phones, then click Options next to the phone you want to change and choose Edit. You may not see a scrollbar on the window that pops up, but you need to scroll down to the Outbound ID section and click the dropdown menu.