I just recently set up a server with the exact same configuration: Ubuntu 18.04 and php 7.2. I just installed the php-sybase module, which includes support for SQL Server thru the pdo_dblib module.
sudo apt-get install php7.2-sybase
check to make sure the module is installed:
$ php -m | grep pdo_dblib
Output:
pdo_dblib
Set up a connection within app/database.php using the driver sqlsrv
'my_connection' => [
'driver' => 'sqlsrv',
...
]
Then go ahead and test the connection:
dd(DB::connection('my_connection')->getPdo());
You might need to check your freetds configuration (should be installed by default) at /etc/freetds/freetds.conf
You might need to adjust the tds version configuration to have work properly with whatever SQL Server version you're connecting to. I think 7.3 is the default.