You are using phpFox version earlier than 4.6.0? Please refer instruction for this article here.

The phpFox script gives you full control over attachments. This tutorial will help you learn how to add, edit and manage attachments for your site.

Adding Attachment Types

Editing Attachment Types

 

Enable or Disable Attachment Types

Managing Attachment Thumbnails

Managing Thumbnail Size

Managing Attachments (v4.6 and up)

Always clear cache after making any changes.