Manage Blob in php

Edit: I actually send the file in a blob to the server, but although I try to handle it I only get a text file.

file_put_contents($target_dir, $_FILES["archivo"]["name"]);

I have a controller in javascript and one of its functions I have in the variable data a file that I pick up from a form.

My question is how do I access this file from a php file, in order to send it to the server?