FIG. 1 is a perspective view of a back plate with pouch for a mobile phone device showing our new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a rear elevational view thereof;

FIG. 4 is a top plan view thereof;

FIG. 5 is a bottom plan view thereof;

FIG. 6 is a left side elevational view thereof;

FIG. 7 is a right side elevational view thereof; and,

FIG. 8 is a back perspective view thereof with pouch shown slightly extended to accommodate a headset.

The broken lines and the features depicted in broken lines throughout the drawing figures form no part of the claimed design. The headset and the remainder of the mobile phone device depicted in broken lines in FIG. 8 form no part of the claimed design.