Unfortunatey, some Yahoo! product features (like those listed below) can only be accessed via desktop computer:

• Editing Yahoo! Mail options
  • Adding/editing folders
  • Modifying spam settings
  • Blocking email addresses
  • Creating vacation responses, etc.
• PC to PC phone calls
• Reactivating dormant Yahoo! Mail accounts
• Creating non-photo email attachments (iOS devices)
• Viewing full email headers