Sharp UX-305 Operation Manual page 82

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.
80
5 5
5 1
START/MEMORY
Step 3 or
2 4
3
(Example)
STOP