Final answer:
The nurse should withhold the phenytoin until the tube feeding is complete.
Step-by-step explanation:
The nurse's best course of action would be to withhold the phenytoin until the tube feeding is complete. Phenytoin is a drug that is not easily absorbed from the gastrointestinal (GI) tract into the bloodstream. Therefore, it would be more effective to administer it through a parenteral route, such as intravenous injection, when the client is not receiving continuous tube feeding via gastrostomy tube.