The ornamental design for a cellphoneholder, as shown and described.
FIG. 1 is a front perspective view of a cell phone holder showing my new design;
FIG. 2 is a left side view of the cell phone holder in its extended and first rotated position;
FIG. 3 is a front view of the cell phone holder in its extended and first rotated position;
FIG. 4 is a rear view of the cell phone holder in its extended and first rotated position;
FIG. 5 is a top view of the cell phone holder in its extended and first rotated position;
FIG. 6 is a bottom view of the cell phone holder in its extended and first rotated position;
FIG. 7 is a left side view of the cell phone holder in its retracted and first rotated position;
FIG. 8 is a left side view of the cell phone holder in its retracted and second rotated position; and,
FIG. 9 is a perspective view of the cell phone holder in its extended and first rotated position as used by a user to hold a cell phone.
Right side views of the cell phone holder not shown are mirror images of left side views. The broken lines depict environmental structure that form no part of the claimed design.