FIG. 1 is a top, rear, and right side perspective view of a plunger holder showing my new design, the broken-line disclosure of a plunger and portion of a floor surface are for illustrative purposes only and form no part of the claimed design;

FIG. 2 is a front elevational view thereof, the broken-line disclosure of a logo is for illustrative purposes only and form no part of the claimed design;

FIG. 3 is a right side elevational view thereof, the left side being a mirror image of that shown;

FIG. 4 is a rear elevational view thereof;

FIG. 5 is a top plan view thereof; and,

FIG. 6 is a bottom plan view thereof.