How to get PHP password_hash function on Ubuntu 12.04 Server

[osx]

I've been reading about the password_hash function of PHP 5.5 and would like to implement it on a 64-bit install of Ubuntu 12.04 server; however, 12.04 uses PHP 5.3 which does not include the password_hash function.

EDIT: I found out that a compatibility pack exists to enable the password_hash function in PHP versions 5.3.7 and later. Now I know the answer to my question, just need to figure out how it is done.

Thanks.