PHP Variables sizes

Is there a maximum size for a variable in PHP. A client of mine is having problems working with a file of around 4Mb. Not really being a php developer I cannot really answer him. To quote him: We are not uploading excel from ftp. We are reading excel file which is about 4 MB. In php settings maximum size of any variable is set to 2 MB so this setting has to change. As any file reading in a variable will only read up to 2 MB and then it will stop. I wasn't aware of any setting that allows you to change the max variable size. Can anyone shed any light on this? Cheers, David.