Just copy and paste the following codes and execute them.
cd /usr/local/share && wget https://bitbucket.org/ariya/phantomjs/downloads/phantomjs-2.1.1-linux-x86_64.tar.bz2 && tar xjf phantomjs-2.1.1-linux-x86_64.tar.bz2 && ln -s /usr/local/share/phantomjs-2.1.1-linux-x86_64/bin/phantomjs /usr/local/share/phantomjs && ln -s /usr/local/share/phantomjs-2.1.1-linux-x86_64/bin/phantomjs /usr/local/bin/phantomjs && ln -s /usr/local/share/phantomjs-2.1.1-linux-x86_64/bin/phantomjs /usr/bin/phantomjs && which phantomjs && phantomjs --version
You should get something like the following: