A true form control listbox can be resized just by right-clicking on
it and then resizing it like any rectangle.
If you mean a form control combo-box, a box that drops down so many
lines when you activate it, that can be sized by right-clicking on it
and picking "Format Control" and then on the Control tab you will find
a setting for "Drop down lines:"
If you mean the drop-down box that appears when you enable data
validation on a cells contents, there is no setting to control the
length of the drop-down box on that control. At least not that I have
ever seen.
