Once I read about the word, religion, in a dictionary. It said something like "worship of the highest". Well, it really depends on what we consider the highest. If we consider Dhamma the highest then it could be a religion in that we show faith and gratitude towards the highest.
Buddhism is also a philosophy, yes, but as it is practiced in many Theravadin and other Buddhist countries, it is also a religion and it's good to put our eyes on the highest and try to purify our mind.
If you consider the Law of Kamma as an impersonal type of "God", it's a matter of what you call "God", then it could be called a religion, but it's a philosophy in that we can understand the Law of Kamma experientially when we begin to contemplate it. However, if we consider that Kamma occurs for more than one lifetime then Buddhism could be considered a religion because we have to take this on faith, we don't actually know that Kamma stays with us from lifetime to lifetime. In fact we do not know for sure that rebirth is true. In that way we contemplate things we don't know to be true and need to take on some degree of faith, which is similar to religion.
It is a philosophy in the sense that we correct our living and life when we investigate the Law of Kamma on a day to day experiential level, but it is a religion if we do this on a lifetime to lifetime level. So it could be both, depends on how you use these words and what you consider religion to be.
For many people in the world, money is their religion, they consider that the highest. The religion of materialism is a very strong religion at present, they have strong beliefs, they have certain beliefs. They say, "when you die, you die", but we don't really know whether that is true, either. So materialism could be considered a religion, also.