Old RPM of version 5.1.56 are still available for download in the archives (manual installation).

New RPM of PHP 5.3.6 (release -3) are build with this new MySQL version.

If you wish to update PHP, without upgrading MySQL, this is possible, you just need to install the version 5.5 of the client library before PHP.

yum --enablerepo=remi-test install compat-mysql55