Phrenic nerves does not arise from the brachial plexus.
The brachial plexus is a network of nerves (formed by the anterior rami of the four cervical nerves and the first thoracic nerve (C5, C6, C7, C8, and T1). This plexus extends from the spinal cord, through the cervicoaxillary canal in the neck, over the first rib, and into the armpit.
It provides unique and functional nerve fibers to the chest, shoulder, arm, arm, and arm. Learn more at Wikipedia.