ssh2_sftp_readlink

<?php
$connection = ssh2_connect('shell.example.com', 22);
ssh2_auth_password($connection, 'username', 'password');
$sftp = ssh2_sftp($connection);

$target = ssh2_sftp_readlink($sftp, '/tmp/mysql.sock');
/* $target is now (e.g.): '/var/run/mysql.sock' */
?>