Well, I'm not a psychologist, but your phobia may have something to do with how your parents reacted to your emerging sexuality. Your mother pretty much threatened abandonment over it, you were aware of your father's sexual violence towards your mother, and your father vented his sexual frustrations to you at a young age. Sounds like a recipe for some negative feelings about sex.

Could it be that the obscene things you mentioned only "seemed" obscene because your mother made you feel so badly about it?

Your phobia beginning when your daughter was about 7, might have been some kind of protective reaction towards her, since she was getting closer to the age when she would be exposed to peer pressure regarding sex. It is difficult to know how relevant your daughter is in all this, but she very well could have been some kind of trigger. Old, painful feelings will sometimes hide for years, until some kind of catalyst brings it to the surface.

Anyway, this is all guess work here. You could find a good therapist (of the psychoanalysis variety) to talk with about this in more depth, so maybe you will get to the heart of what is making you feel this way. Or, you are welcome to continue talking with me about this if you want. I would just keep asking more questions, so we can maybe narrow it down further.