From my experience, connect to Oracle DB on remote server :
First, u should install Oracle client on your web server. Check manual from Oracle or u can read from http://callista.free.fr/php_oracle
Then, if U use Windows + Apache + PHP, uncomment the loadable extensions oci8.dll on php.ini (make sure the path to loadable extensions is correct).
If U use Linux(RH) + Apache + PHP, u should reconfigure PHP to support oci8. In this case, I still work on error Ora-12154. I just trying to solve this error. I think just relate to TNS problems.