I needed to move a file to another folder regardless if that file existed in the target already so I wrote a small piece to append a unique number to each file.
$rem = $_GET['file'];
$ticket = uniqid(rand(), true);
rename("$rem", "www/home/storefile/$ticket$rem");
the output looks like this - 6881432893ad4925a1.70147481filename.txt
This also helps if you want different versions of the file stored.