phprms is a library that allow you to access RMS file located on a VMS server using php 3. If you don't know what all this mess is, you don't need it.
In fact, phprms is just a wrapper for librms written by Patrick Cauldfield. As a result, it will only works under linux.
You can download the source for php3 here
If you prefer php4, Eric Terstegen has port the library to php4, it's available here