I have been using Grunt with Handlebars and Assemble.io, SASS but I will need to work with PHP pages and database so I am looking for a great tool like Grunt which allows me to use PHP pages / MySql database.
I think Phing is a good choice but why don't you use Grunt for PHP as well? Why would you pick a new tool only for PHP?
(you could install grunt-php, grunt-phpunit, grunt-phpmd, grunt-phpspec, grunt-phplint and so on ... you might start with this)
List of useful links to integrate grunt with Yii: