A Phase Space is a space of all possible states of a system. For example, in classical (non-Quantum) mechanics, a pendulum might have a dimension representing the position along the pendulum's path and a second dimension its momentum, forming its Phase Plane. Phase Line similarly indicates just a single dimension of states.
For an object moving in (3-dimensional) space, it could be six dimensions, three for position and three for momentum. The object would represent a point in this phase space.
A Phase Integral is an integral calculating a volume in a phase space. For some calculations, such volumes is useful as a substitution for discrete numbers of potential points in the phase space.