This software is distributed as-is, under the terms of the GNU General Public License version 3 or, at your option, any later version of the license published by the Free Software Foundation. You can read the full text of the license, as published by the Free Software Foundation, on-line at http://www.gnu.org/licenses/gpl.html.
You do not need separate access to the source code of the software. The PHAR format is just an archive file with metadata. You can easily extract it to get the full source code of the software. If you are not sure how you can extract a PHAR file, search on the web. That said, if you do need access to the source code you should already be familiar enough with PHP to know how to do this trivial task.