Just push a new version of the plug-in. It now use the subprocess library, and call directly pear php_beautifier, so it should resolve the problem with MacOS (not tested yet, need feedback).
The plug-in currently format all current file content and I redirect stderr to a custom panel (so no more errors in place of the code \o/).
The next step is a decent config file with configurable php_beautifier path and filter. You can also edit the options directly in the python file. Default options are :
indent = "-s4" # 4 spaces
filters = "ArrayNested() NewLines(before=switch:while:for:foreach:T_CLASS:return:break) Pear(add-header=false)"