My company uses the sqlserv extension to connect to a MSSQL database. This extension was chosen over the mssql extension because it is actively being maintained by Microsoft
You cannot run the SQLSRV extension on anything other than Windows as stated here:
http://php.net/manual/en/sqlsrv.installation.php
However, even if you could, I would strongly urge you to stay away from the SQLSRV extension as it is extremely buggy and underdeveloped. You would be much better off using PDO!
I spent days trying to work out which extension to use, and after much research and questions on stackoverflow, it was clear that PDO was the only realistic solution for connecting to an MSSQL database. Not to mention the additional functionality that you have!
Try and execute stored procedures, return multiple recordsets along with output parameters using the SQLSERV extension!! Just one of the many features that can be done in a few lines with PDO but cannot be done with SQLSERV.
Furthermore, PDO is faster!