Saying you ‘broke’ it isn’t really correct.
When you fracture the penis you bend the fluid-filled compartments that keep it erect, and it means they burst and blood fills the penis in a strange place outside the usual blood-filled space- like popping a balloon full of water. The penis looks bent when erect because it no longer has the pressure of the blood in a tube to keep it straight, and goes purple as the blood flows closer to the skin’s surface.
While the penis has no bones in humans, it still has structures designed to be rigid during erection. If the penis is bent sharply during intercourse, or some other reason, then the tubes inside the penis responsible for semen and urine release can be damaged.
This can include an audible cracking sound, very similar to that of a broken bone, as well as the potential for permanent changes in the shape of the member or ability to become erect.