Each phrase that appears on a page is a potential keyphrase, so you there is an unlimited number of phrases your page will be found for. But you should probably only deliberately target 2 or 3 phrases per page.
Theoretically speaking, you can put as many as keywords you can in a page. But too many keywords will dilute the importance of your targeted keyword. Better put more weight on 2-3 keywords in a page, but also show up 5-10 other keywords in case users will forget them.