Phrenic nerve is
Phrenic nerve is a mixed nerve, mainly arises from 4th cervical nerve. It lies behind prevertebral fascia and in front of scalenus anterior.
Motor nerve to diaphragm
Arises chiefly from 3rd cervical nerve, also receives contribution from 4th and 5th cervical nerves
The nerve runs vertically on the anterior surface of scalenus anterior
It lies anterior to prevertebral fascia