Sharp FO-475 Operation Manual page 90

Blocking Reception of Unwanted Faxes
4
Enter the full number you want to block
(max. of 20 digits).
5
Press the START/MEMORY key.
6
Return to Step 3 to enter (or clear)
another number, or press STOP to exit.
78
5 5
5 1
START/MEMORY
STOP
Step 3 or
2
3 4
(Example)