'Form' in the Bible

who, although He existed in the form and unchanging essence of God [as One with Him, possessing the fullness of all the divine attributes—the entire nature of deity], did not regard equality with God a thing to be grasped or asserted [as if He did not already possess it, or was afraid of losing it];

After He was found in [terms of His] outward appearance as a man [for a divinely-appointed time], He humbled Himself [still further] by becoming obedient [to the Father] to the point of death, even death on a cross.