It's actually a enlarged clitoris, and it serves the same purpose of a clitoris in other animals—sexual stimulation.

Hyena females are considerably larger than the males. The females are masculinized due to the excess testosterone in their bodies; they have more testosterone in their bodies than most male hyenas. As a result of this masculinization, females are a third larger than the males, have more muscle mass, are more aggressive, and have masculinized genetalia. Their vulva is fused to look like a scrotum and testes, and their clitoris is large and looks like a phallus, and can be erected just like a penis. The vagina runs through the pseudo penis. This makes it hard for them to mate and give birth, since they do so through this pseudo penis. It was once thought that hyenas were hermaphroditic animals because the females sported genitalia similar to the males. In fact, the only sure way to determine the sex of a hyena is that after giving birth the female's two black nipples become enlarged. The erect 'penis' of both sexes plays a prominent role in ritualized greeting

The "false penis", which is actually a fusion of the clitoris and labia of the vagina, seems to be used in dominance displays and to indicate aggression and willingness to fight. Female hyenas dominate over males in many cases, and they behave in the way that male wolves do when establishing pack heirarchy: they often "mount" subordinate animals, and an "erection" indicates they are confident of being able to take on a challenger in a fight. Their rather unique genitalia, and the accompanying high levels of "male" hormones, is probably very much connected to their social order and dominance structure. As with wolves, usually only the dominant one or two hyenas in a pack breed in a year. Levels of testosterone are connected to dominance and aggression; and it is likely that the most "male-like" of the females were traditionally the ones that fought their way to the top of the pack, and thus bred. Over the generations this would have selected females closer and closer to the male model, until they became more "male" than the males. This said, it is not without cost. The first pups a hyena female has have to rip the psuedo-penis open in order to be born; these pups are almost invariably suffocated during the process, and it is not unknown for the hyena mother herself to sustain too much trauma and die of it.

the female hyena has what looks like a penis and testicles. The female actually uses this mock penis to deliver their cubs :) lol i watched nat geo last night about it

Mostly men get hyenas, since men tend to lift more weights and women tend to do more cardio