Running PHP 7.2 on IIS 10, I had to use the IIS Web Platform Components wizard to install the Microsoft PHP drivers version 5.2 x64 to get this command to work. Manually installing 4.0 drivers did not work.
The SQLSRV extension is enabled by adding appropriate DLL file to your PHP extension directory and the corresponding entry to the php.ini file. The SQLSRV download comes with 8 driver files, four of which are for PDO support.
The most recent version of the driver is available for download here: » SQLSRV download.
For more information about SQLSRV requirements, see » SQLSRV System Requirements.
Since version 4.0 the SQLSRV extension is compatible only with PHP 7.0 running on Linux or Windows.
Running PHP 7.2 on IIS 10, I had to use the IIS Web Platform Components wizard to install the Microsoft PHP drivers version 5.2 x64 to get this command to work. Manually installing 4.0 drivers did not work.
PECL packages for Linux SQLSRV and PDO_SQLSRV drivers (4.0.7) are available now.
https://github.com/Microsoft/msphpsql/releases
SQLSRV doesn't use mssql_connect - it is it's own extension, therefore to connect you'd use sqlsrv_connect:
http://www.php.net/manual/en/function.sqlsrv-connect.php