The ornamental design for a cellphoneholder, as shown and described.
FIG. 1 is a perspective view of a cell phone holder showing my new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a left elevational view thereof;
FIG. 5 is a right elevational view thereof;
FIG. 6 is a top view thereof;
FIG. 7 is a bottom view thereof; and,
FIG. 8 is a perspective view of the cell phone holder viewed from another direction.
The broken lines, and unshaded surfaces surrounded by broken lines, illustrate portions of the cell phone holder that form no part of the claimed design.