If by "feel sexier" they mean "are more likely to be sexually proceptive or receptive," then it turns out no, women don't necessarily feel sexier at ovulation. Some women do. Others feel sexy right before menstruation or right after menstruation. For others, their interest in sex has no reliable relationship to their cycle. It's one of the complex things about human female sexuality is that it appears to be largely decoupled from their hormonal oscillation. There is some evidence of behavior changes like walking more and changes in clothing choice, but no particularly compelling explanation for why these things might be true. Just, like, FYI.

Alas, though the word upsuck is lots of fun, the upsuck theory has been thoroughly debunked. See Elisabeth Lloyd truly wonderful "The Case of the Female Orgasm" for a relentlessly specific account.