$ yum list php56w-mssql
Installed Packages
php56w-mssql.x86_64            5.6.30-1.w7        @webtatic

$ cat /etc/php.d/mssql.ini
; Enable mssql extension module
extension=mssql.so

$ php -i | grep 'PDO drivers'
PDO drivers => dblib, mysql, sqlite

$ yum list php56w-odbc
Installed Packages
php56w-odbc.x86_64    5.6.30-1.w7    @webtatic

$ cat /etc/php.d/odbc.ini
extension=odbc.so

$mssqldriver = 'ODBC Driver 13 for SQL Server';
$hostname='1.2.3.4';
$dbname='foobar';
$username='';
$password='';

$dsn = "odbc:Driver={$mssqldriver};Server={$hostname};Database={$dbname};MARS_Connection=yes";
$pdo= new PDO($dsn, $username, $password);