The ornamental design for a phone holster, as shown and described.
FIG. 1 is a front perspective view of a phone holster showing my new design as worn by a person; it being understood that the broken lines are for illustrative purposes only and form no part of the claimed design;
FIG. 2 is an enlarged view of the design of FIG. 1.
FIG. 3 is a rear perspective view of the design of FIG. 2.
FIG. 4 is an enlarged top plan view of the design of FIG. 1; and,
FIG. 5 is an enlarged front perspective view of the belt clip portion of the design of FIG. 1.