In order to obtain the citation styles, go to this site and download them. Afterwards, you have to open Zotero and go the Settings menu. From there, you select “Cite” and get a list of all currently imported citation styles.
This should look like this:
You can then add the Phenotero styles by clicking on the Button labelled with a “+” and then selecting the csl-file you just downloaded. You have to repeat the last step separately for each of the styles you wish to import.