what are the main constraints on this project? does it have to be in php, does it have to be hosted on your infrastructure, host ... on your side?
I could tell you two solutions that could be integrated with your php website (in case you have wordpress or joomla). Well actually maybe another important question is are you going to have secure download implemented? you know, this is a game changer in case you need it and that was may assumption.
If you need sharing like open sharing, upload doc and here's the link in case anyone would want to take a look ... that would simplify a little bit