Please first Download Quercus.
Quercus say :

Quercus is Caucho Technology’s 100% Java implementation of PHP 5 released under the Open Source GPL license. Quercus comes with many PHP modules and extensions like PDF, PDO, MySQL, and JSON. Quercus allows for tight integration of Java services with PHP scripts, so using PHP with JMS or Grails is a quick and painless endeavor.

Please follow bellow lines :

• mkdir -p /opt/downloads
• wget -o /opt/downloads/quercus-4.0.3.war http://caucho.com/download/quercus-4.0.3.war

Install Quercus as a shared library :

• unzip -j /opt/downloads/quercus-4.0.3.war \\*.jar -d /opt/tomcat/lib

Enable PHP support for the virtual hosts by installing the quercus web.xml. For each virtual host execute:

• unzip /opt/downloads/quercus-4.0.3.war *web.xml -d /opt/tomcat/webapps.mydomain.com/ROOT

Now restart Tomcat :

• /etc/init.d/tomcat start

Be careful : This warfile just work for PHP 5 or higher