You'd use $_FILES['uploaded_file']['tmp_name']
, which is the path where PHP stored the uploaded file (it's a temporary file, removed automatically by PHP when the script ends, unless you've moved/copied it elsewhere).
Assuming your client-side form and server-side upload settings are correct, there's nothing you have to do to "pull in" the upload. It'll just magically be available in that tmp_name path.
Note that you WILL have to validate that the upload actually succeeded, e.g.
if ($_FILES['uploaded_file']['error'] === UPLOAD_ERR_OK) {
... attach file to email ...
}
Otherwise you may try to do an attachment with a damaged/partial/non-existent file.