The phallic stage, the third phase of psychosexual development (ages 3-6), is when the genitals become the primary erogenous zone and children notice the physical differences between sexes. The central conflict involves a child's desire for the opposite-sex parent and rivalry with the same-sex parent. For boys, this manifests as the Oedipus complex, while for girls, it involves the Electra complex and what Freud termed penis envy. Unresolved conflicts in this stage can lead to fixation, potentially resulting in a vain and overly ambitious adult personality.