Sharp FO-475 Operation Manual page 21

Extension phone (optional)
If desired, you can connect an extension phone to the TEL. SET socket on
the fax.
1
Remove the seal covering the TEL. SET
socket.
2
Connect the extension phone line to the
TEL. SET socket.
Important: In New Zealand, not all standard telephones and answering
machines will respond to incoming ringing when connected to the extension
socket of the equipment.
Connections
9