PHP function ssh2_connect is not working

I have installed the SSH2 PECL extension and its working fine thanks all for you help...

I have solved this on ubuntu 16.4 PHP 7.0.27-0+deb9u and nginx

sudo apt install php-ssh2 

Honestly, I'd recommend using phpseclib, a pure PHP SSH2 implementation. Example:

<?php
include('Net/SSH2.php');

$ssh = new Net_SSH2('www.domain.tld');
if (!$ssh->login('username', 'password')) {
    exit('Login Failed');
}

echo $ssh->exec('pwd');
echo $ssh->exec('ls -la');
?>

It's a ton more portable, easier to use and more feature packed too.