The ornamental design for a smartphonechestholster, as shown and described.
FIG. 1 is a front view of a smartphone chest holster showing my new design;
FIG. 2 is a rear view of the smartphone chest holster;
FIG. 3 is a right side view of the smartphone chest holster;
FIG. 4 is a left side view of the smartphone chest holster;
FIG. 5 is a top view of the smartphone chest holster;
FIG. 6 is a bottom view of the smartphone chest holster; and,
FIG. 7 is a top front side perspective view of the smartphone chest holster in use.
The broken lines in FIG. 7 are illustrative of environmental structure forming no part of the claimed design. The broken lines on the straps represent stitching which forms no part of the claimed design.