How to disable Keynote access on my iPhone

There is no known way (at least that I'm aware of) to hack an iPhone via Keynote (there are precious few ways to do it at all, let alone through Keynote)

Keynote is, ostensibly, a presentation app. Not sure what mechanism would even exist for this to compromise your phone, although crazier things have happened..

I'd step back first, though, and ask... what makes you think that Keynote is responsible for your phone getting hacked?