Auto File Rename while Uploading – For Example: 00004001, 00004002, 0000400

I am new to PHP and I need some help in the below code. The below code is working fine but I need to add a "Functionality to be added in the below code, so that if any New File is uploaded it should auto increment in a series. For Example: 00004001, 00004002, 00004003.... and so on.

Please help...! Below is the existing code. Currently it Uploads the exact file name to the remote server.

<?php
if ( empty( $_FILES['file'] ) ) {
    return;
}
$ftp_server = "xx.xx.x.xxxx";
$ftp_user_name = "xxxxxxx";
$ftp_user_pass = "xxxxxxxxxxxxxxxxxxxxxxxxxx";
$destination_file = "";
$source_file = $_FILES['file']['tmp_name'];

// set up basic connection
$conn_id = ftp_connect($ftp_server);


// login with username and password
$login_result = ftp_login($conn_id, $ftp_user_name, $ftp_user_pass); 

//ftp_pasv($conn_id, true); 

// check connection
if ((!$conn_id) || (!$login_result)) { 
    echo "FTP connection has failed!";
    echo "Attempted to connect to $ftp_server for user $ftp_user_name"; 
    exit; 
}   else {


    echo "<p align=center> Your Image has been Uploaded if you dont't see any Error Msg Below</p> ";
}

// upload the file

$destination_folder = "/";
$destination_file = $destination_folder . "/" . basename($_FILES['file']['name']);
//ftp_put($conn_id, $destination_file, $source_file, FTP_BINARY); 
$upload = ftp_put($conn_id, $destination_file, $source_file, FTP_BINARY); 

// check upload status
if (!$upload) { 


echo "<p align=center> **File Upload Has Failed &#128558</p> ";

} else {
echo "";
}

// close the FTP stream 
ftp_close($conn_id);
?>