Historical events that are not empirically or factually known, especially when they involve supernatural elements or communication with God/gods or supernatural beings are technically considered myths. We have no scientific proof that any of the miracles or communications with God that are recorded in the Bible actually happened. It's hard enough to prove current-day miracles scientifically. Therefore, it's fair to categorize many the stories of the Bible as myths, even though to many people, they're actual historical accounts. What Philemon probably meant by what he said is that Christianity is based on a myth.
Personally, I believe most of what the Bible says actually happened, although I'm not convinced that the explanations or interpretations are all correct, neither by the original authors nor the translators. Even the books themselves that were chosen for inclusion by the Catholic Church around AD 400 have been altered, and don't include many other texts that circulated among early Christians at the time.
I think a lot of the events that were attributed to God, especially in the Old Testament, were actually perpetrated by the people themselves or blown out of proportion. Some of what the Bible says, I believe, was not meant to be taken literally - especially Revelations. I'm of the view that Revelations describes a personal journey of faith rather than fortelling global events.
I do believe in the story of Jesus - virgin birth, miracles, crucifixion, resurrection. But I also acknowledge that that story is not unique to Jesus, but there are other historical figures who have parallel stories.
The one thing I take from Christianity, that I think is one of the most important elements, comes from Jesus's last speech at the Last Supper. He talked about sending a Spirit of Truth, a comforter, who everyone could access, and by that, we would all be able to do everything Jesus was able to do, and more. This is what many people (myself included) consider the Higher Self. Through that mechanism, everyone is able to access and perceive truth directly without having to rely on intellectual understanding of a book written in a dead language that continues to be manipulated and abused by people in attempts to secure power and keep people enslaved by fear.