Solved my issue:
Run:
sudo tar jxf /opt/kibana/installedPlugins/x-pack/reporting/.phantom/phantomjs-1.9.8-linux-x86_64.tar.bz2.
Next, restart Kibana:
sudo service kibana restart.
So from what I gather this particular plugin drops a version for each platform (windows, linux, etc.). Next it attempts to extract the package for the appropriate platform. Unfortunately it does not have the proper permissions to execute tar.
Hope this is helpful to anyone else wanting to check out the Elastic Stack 5.0 release early.