Do you have a file /etc/httpd/conf.d/php.conf This file located in this directory loads php when the Apache or httpd service is started on Centos. If you do not have this file which should have been installed automatically by default when you did the yum install php programs.
If it is not there, google install php on centos 7 it will instruct you step by step how to install it. OCS requires php and a whole lot more.