The PHP Coding Standards Fixer (PHP CS Fixer) tool fixes your code to follow standards; whether you want to follow PHP coding standards as defined in the PSR-1, PSR-2, etc., or other community driven ones like the Symfony one. You can also define your (teams) style through configuration.
It can modernize your code (like converting the pow function to the ** operator on PHP 5.6) and (micro) optimize it.
If you are already using a linter to identify coding standards problems in your code, you know that fixing them by hand is tedious, especially on large projects. This tool does not only detect them, but also fixes them for you.