If you are relating to a display file, then just type DSPATR(ND) just below the text description of that field.
Condition this field with an indicator like for eg :- if *99 is on then Display the field else hide it. Populate this field with your Physical file field. Change the values of the indicator in your program according to your requirement.
One approach is to hide the fields through a logical file
- Physical file is created with all fields
- Logical file is created over the physical listing only the fields you want to provide access to.
- Physical file may be resricted by security.