By default, phantomjs will be downloaded from https://bitbucket.org/ariya/phantomjs/downloads, but if for some reason bitbucket is down, a firewall/proxy is blocking bitbucket or http://cnpmjs.org/downloads contais corrupted files, use:
npm install phantomjs --phantomjs_downloadurl=https://github.com/msempere/phantomjs-repo/releases/download/v1.9.8/phantomjs-1.9.8-linux-x86_64.tar.bz2