php - I use Dropzone for upload multiple image but I need to rename file sort by number

one text

First I use Dropzone and I need to upload into my folder by sort number.

upload 4846541.jpg to change 1.jpg
next upload 897412.jpg to change 2.jpg

I use php move file upload:

if (!isset($_FILES["file"])) {
    die("noooo.");
} else { 
    if ( move_uploaded_file(['file']['tmp_name'], "images/".$sortbynumber) ) {
        echo 'ok';

I need $sortbynumber is sort by 1, 2, 3 by check isset file in folder if it's have and next 2.jpg.

I'm sorry for my bad english T_T help me pls

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