phase an-gle
/feɪz ˈæŋ.ɡəl/
noun
The angle between the light from the sun and the light reflected from an observed object and it ranges from 0 to 180 degrees.
Example:
The Moon at full phase has a phase angle close to 0°.
At new Moon, the phase angle is close to 180°.
Source: Cindy McKean