Sharp UX-310 Operation Manual page 54

Receiving Documents
3
If the other party first talks and then wants to send a fax, press the
START key after speaking (press your START key before the
sender presses their Start key).
Make sure that the display shows RECEIVING, then replace the
handset.
Answering with an extension phone
1
Answer the extension phone when it rings.
2
If you hear a fax tone when you answer an extension phone, wait
until your fax answers (the extension phone will go dead), and then
hang up.
3
If the fax doesn't respond, or if the other party first talks to you and
then wants to send a fax, press 5, *, and * on the extension phone
(only on a tone dial phone). This signals the fax to begin reception.
Hang up.
52
START
Beep
Phone goes dead
5
RECEIVING