GNU Multiple Precision Arithmetic Library (GMP) on Ubuntu 12.04 LAMP Server... how to?

I've got a newly installed Ubuntu 12.04 LAMP Server set up to host Drupal sites. Its up and running fine, but on any site that has the OpenID Module enabled, the site status page reports:
"OpenID suggests the use of the GMP Math library for PHP for optimal performance. Check the GMP Math Library documentation for installation instructions."
The documentation linked to is not very helpful with regards to installing the GMP on an Ubuntu server (http://php.net/manual/en/gmp.installation.php)... but after doing some digging I *think* I learned that I have to install the gmp libraries and then compile php with gmp myself, rather than simply use apt-get install... But I really don't want to break the existing LAMP installation by messing around with compiling php myself.
So far I've installed libgmp-dev, libmpfr-dev, and libmpc-dev. Is there a simple way to install t gmp? If I compile php myself, what will happen to the existing php configuration?