$configurator = (new \Phuxtil\Flysystem\SshShell\SshShellConfigurator())
    ->setRoot('/remote_server/path')
    ->setUser('remote_user')
    ->setHost('remote-ssh-host')
    ->setPrivateKey('path/to/id_rsa.private_key')
    ->setPort(22);

$configurator = (new \Phuxtil\Flysystem\SshShell\SshShellConfigurator())
    ->setUser('user')
    ->setHost('host');

$configurator = (new \Phuxtil\Flysystem\SshShell\SshShellConfigurator())
    ->setUser('user')
    ->setHost('host')
    ->setPrivateKey('path/to/id_rsa.private_key');

<?php

use League\Flysystem\Filesystem;
use Phuxtil\Flysystem\SshShell\SshShellConfigurator;
use Phuxtil\Flysystem\SshShell\SshShellFactory;

\error_reporting(\E_ALL);

include __DIR__ . '/vendor/autoload.php';

$configurator = (new SshShellConfigurator())
    ->setRoot('/tmp/remote_fs')
    ->setUser('user')
    ->setHost('host');

$adapter = (new SshShellFactory())->createAdapter($configurator);

$filesystem = new Filesystem($adapter);