A new TLF yum repository has been created for Red Hat Enterprise Linux 6-based distributions (ie CentOS 6). As of right now, there is only a 64-bit repo. 32-bit packages are forthcoming. php 5.3.6 packages are available here by running the following set of commands:
rpm -Uvh http://yum.thelinuxfix.com/RHEL/6/x86_64/tlf-release-1-2.el6.noarch.rpm
yum install php php-mysql php-cli php-mbstring
There are several php packages available and the above yum command is only an example if you wanted to install php, the cli, and the mysql and mbstring extensions. The extensions you need will be based upon your usage.