How do you call people with fake legs?

People who have artificial legs are physically challenged, so we do not CALL them anything, except 'Sir' or Ma'am' if they are strangers; if they are friends they must have names, so you call them by their NAME.

If a person has lost a limb, health professionals would describe them as an amputee; if they've lost both legs they'd be described as a double amputee. But you would never refer to them in this way unless it was necessary for descriptive medical reasons; you'd speak to and of them as above.