Could a fleet enema (sodium bisphosphate) give you diarrhea?

Temporarily: A fleets enema causes the colon to evacuate. Most often this simply results in evacuation of the solid stool within the distal colon, but it may cause the more liquid stool from the more proximal colon to reach the rectum "ahead of schedule" resulting briefly in diarrhea. This should clear fairly rapidly and not cause any persistent problems.

Fleets enema: Absolutely. It is a saline laxative and draws water into the colon and causes diarrhea. Its effects are limited and should only provide a transient diarrhea.