Chris White has a post to his site sharing a method he's come up with to avoid the burden of file uploads in your PHP application with the help of the offerings of Amazon S3 and some creative coding.

Handling file uploads sucks. Code-wise it's a fairly simple task, the files get sent along with a POST request and are available server-side in the $_FILES super global. Your framework of choice may even have a convenient way of dealing with these files, probably based on Symfony's UploadedFile class. Unfortunately it's not that simple.

[...] For most situations using S3 is a no brainer, but the majority of developers transfer their user's uploads to S3 after they have received them on the server side. This doesn't have to be the case, your user's web browser can send the file directly to an S3 bucket. You don't even have to open the bucket up to the public. Signed upload URLs with an expiry will allow temporary access to upload a single object.

He points out two advantages of this method: that you don't have to handle the upload part of file uploads and that it gives the user more control. He shares a video of the end result (a simple file upload frontend) and the code that you'll need to use the AWS PHP SDK to make it all work together. There's some configuration changes that'll need to be made on the S3 bucket side (like for CORS) but the code itself to make the connection is relatively simple. He does a great job of explaining every step of the way and includes the Javascript needed for the frontend as well.