There's an article somewhere on PHPBuilder that covers uploading images [do a search on mysql and images and you should find it], and the last page of that covers problems with uploaded objetcs larger than 1Mb.
IIRC its limits set in MySQL and its interface libraries that cause the problem, not limits in PHP [which I believe would not have problems until around the 2G mark, where you hit the string length limit - andI doubt you'll need files that big]. You can confirm this is the case if PHP can read all the uploaded file but can't put it into the DB.
If you have access rights to tinker with the MySQL server, try that [though it probably isn't recommended]. If not you'll need to do something else with the bigger files [store them in the file system with a pointer to the file in the database?, split them into 1Mb chunks?].
A quick note: loading large amounts of data [like a 1Mb+ upload] into a variable isn't very scalable unless the larger uploads are rare. Remeber that you are holding all that memory until the end of your script, so it isn't available for other scripts/processes, the DB or for disk cacheing.
