Number of Phases (0054,0031) is the number of dynamic phases, independent of the number of Detectors and Isotopes. See Section C.8.4.14 for definition of a phase.

Phase Vector (0054,0030) is an indexing vector. The value of the nth element of this vector is the phase number of the nth frame in this image, and shall have a value from 1 to Number of Phases (0054,0031).