Most philosophers, when they teach the philosophy of religion, actually teach their classes the arguments they regard as the best ones for (and also against) the existence of God. These include several versions of the cosmological argument (in which God figures as the first cause, or as the cause of the universe as we know it), the teleological argument (in which the universe is understood as showing signs of having been intelligently designed, indicating a Designer), and the ontological argument (in which God's existence is argued to be derivable just from the definition or conception of God).

I find the argument that works best with students who are inclinded to be atheists or agnostics is some version of the ontological argument. I usually teach several versions, but here is a version of one of the most famous of those arguments, by Anselm:

Even the atheist grants that God is that being than which no greater can be conceived.
Hence, even for the atheist, God exists at least in the imagination (indeed, the atheist claims that God exists only in the imagination).
But things that exist in reality are greater than things that exist only in the imagination.
So, if God existed only in the imagination, then God would not be that being than which no greater can be conceived--for we can conceive a greater being: one that existed in reality as well as in the imagination).
Hence, as God is that being than which no greater can be conceived, God must exist in reality.

Of course, many philosophers (myself included) do not think that this argument (or any of its many variations) actually prove that God exists. But maybe you can enjoy trying to figure out why most philosophers don't accept this argument! If you can't, then maybe you can ask philosophers again about this!