The PHP version comes in default CentOS 7 repositories is rather horribly outdated. This is problematic when running Wordpress, which has to be upgraded constantly, and really old PHP versions may not be accepted, security-patched or not. The solution is to get updated PHP from the remi yum repositories. There are two sets of PHP packages as described here:

• Install updated packages that replace the old PHP 5 packages (i.e. names are the same)