PhP Curl SFTP File Editing

I am trying to create a online editor for multiple server. I want to edit a custom file on a server and I need to get it via sftp. My current code looks like this:

<?php

$user="user";
$pass = 'pass';
$c = curl_init("sftp://$user:$pass@0.0.0.0/path/to/file/file.txt");
curl_setopt($c, CURLOPT_PORT, 3206);
curl_setopt($c, CURLOPT_PROTOCOLS, CURLPROTO_SFTP);
curl_setopt($c, CURLOPT_FILE, $fh);
curl_exec($c);
curl_close($c);
//the next line is not working and from now on am I stuck
$text = file_get_contents($fh);

?>
<!-- HTML form -->
<form action="" method="post">
<textarea name="text"><?php echo htmlspecialchars($text) ?></textarea>
<input 

type="submit" />
<input type="reset" />
</form>

I want to edit this file on the website and then reupload it to the sftp server in the same directory (overweite the existing one). I do not know how to continue. Thanks for the help.