A figure or symbol of the female organ of generation as an object of veneration among the Hindus and others.I'd prefer to find the Greek-root antonym. I found a discussion board that claims that the two best possibilities are "hysteric" (not a great possibility, for obvious reasons) and "uterine." But I'm not sure that the uterus is the appropriate opposite organ in this case - when we use phallic, we really use it to refer to the physical act of...copulation. I think the antonym should refer to the female portion of the physical interface between man and woman.
I guess I'll conclude for now that yonic is appropriate, because of this note on the etymology from the OED (and because of the general consensus online):
In nature-worship, all natural orifices were reverenced as representing the yoni of the mother-earth goddess.So I don't think yoni refers to the uterus...Sorry if this is an awkward discussion for my less mature readers. But I do plan to start using "yonic" in conversation as soon as possible.