Já experimentou estes passos?:
Install both RPM packages :
rpm -ivh instantclient-basic-linux.XXX.rpm
rpm -ivh instantclient-sdk-linux.XXX.rpm
Install some prerequisite
yum install php-pear yum install php-devel
Download the OCI8 extension
pear download pecl/oci8
tar xvzf oci8-1.4.7.tgz
cd oci8-1.4.7/phpize
Configure the extension with your Oracle client library path (change the path …/11.2/… with your own version) :
./configure --with-oci8=shared,instantclient,/usr/lib/oracle/11.2/client64/lib/
Compile and install
make
make install
Configure SELinux : allows httpd to execute programs that require memory addresses that are both executable and writeable
setsebool -P httpd_execmem 1
Add the folowing configuration at the end of php.ini
vi /etc/php.ini
[OCI8] extension=oci8.so
Restart Apache
service httpd restart
Fonte: link