Will Node js takes over the place of PHP in 2018 completely ?
you should learn that Node just take over the popularity and interest of PHP or PHP will be going more ? because world's most used CMS is PHP
You judge based on usage, Node.js is clearly better, as most people say, since it offers more features and templates/modules (new age of programming). Node.js becoming more and more popular for a reason... PHP existant usage though is higher because it's older and used for a longer period...
Neither Languages will take over or die out soon. Both have different use-cases. Node does things PHP can't do and PHP does things Node can't do.