delete https://api.phone.com/v4/accounts//fax/
Phone.com customers can fax outbound documents via the Control Panel or API; They can also receive incoming fax into one of the Extension mailbox. The Fax API service allows users send a fax, list all fax in the account, change the 'new' status of a fax, download a fax and delete a fax.
Delete an individual Fax record.