I think Meteor has a lot of advantages of PHP. For one, customizing it is easier (in my opinion) than customizing a CMS like Wordpress.
Also, a very big factor you can convince your clients with is the real-time aspect of it. It is real-time by default and if you try to make a PHP-based app real-time, you will have to use a different front end framework to do so. And there is JS on both the server and the client. You only need to know one language and you can do full stack development whereas you would have to find people specifically for front end and others specifically for back end if you did PHP + JS.