$ tar xvjf phantomjs-2.1.1-linux-x86_64.tar.bz2 -C /usr/local/share/

If you have a copy of the ReSpec repository handy, you may see that there is also a respec2html.js tool under tools/. Feel free to try using it instead of the above process, but please note that it is not used much currently and may behave in a somewhat experimental manner (experiences with it vary — but it's worth a shot if you're looking for a way to generate ReSpec output from the command line).