By default, phone and fax numbers are displayed on invoices,
But when it comes to sending invoices:
  • by postal mail, customers might not want their phone numbers to show on the invoice cause it shows in the envelope window. 
  • by fax, you will want to show the sender's fax number.
Here is how to set it accordingly: 
  • On the menu, go to Configuration > Local configuration,
  • Click on the second tab [General Data],
  • Check the box: Do not display phone number on the invoice,
  • Click Save.
Note: This configuration is per-station setting, meaning that every station can have their own setting.