Look at the outside of the package. If you see a heksher, it is koshere. In the case of Kraft brand Philadelphia Cream Cheese, the Kraft Foods pays the Orthodox Union to supervise their cheesemaking, and the OU allows Kraft to print its heksher on the package, so you look for an O with a smaller u inside. That is the OU heksher. Other kosher certifying organizations have other hekshers. Jews who care about Kashrut are usually familiar with a large number of hekshers.