You can use an Opacity Mask:
Note: Boxes have a black fill and white stroke. This is important for the mask to function correctly. Also, make certain the black is 100% black of all colors - that means R0G0B0 or C100M100Y100K100 - if your black isn't a full "rich" black (or registration black), then you'll get some slight bleed through of the number possibly.
Also note, the text in this image is still "live" so the number can easily be changed with the Type Tool and retain the masking.
While the first thought may be a clipping mask, for something as complex as the grid of lines, you would have to expand the strokes and merge them first. And ultimately with the grid it may be too complex to use as a clipping mask. An Opacity mask will do exactly what you want in a less complex manner and should avoid the issues a clipping mask may present.