Looks like a dildo collection.
And I bet this is a lot closer to the truth than most of the guesses. Celebration of sexuality or something politically incorrect like that.
That was my first thought too. Fertility rites seem to be deeply-imbedded in human culture reaching far back into the past. Anything in nature with a phallic appearance might have held deep significance for the Neanderthals. Phallic worship in India goes back to prehistoric times.