A phase space is a space of all possible states of a system, and for mechanical systems the phase space typically considered is a position and a momentum component for each dimension, i.e., six dimensions for 3-dimensional space. Two dimensions are sufficient for the phase space of a pendulum allowed to swing along a single path, one for its position along the path and another for its momentum. The term phase line similarly indicates just a single dimension of states (which would not be for such a mechanical system).
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.