You can try using css to control the visual layout.
I have tested on my dev server and this was successful.
@media only screen and ( max-width: 320px ) {
.gallery-item {float:left;width:50% !important;}
}
what we have done is set the column to 50% the total container width when viewing on devices smaller then 320px. You can adjust this as you see fit.
Simply drop this styling into your themes css via your theme options page. If you do not have one you can also add it to the themes css stylesheet if you have admin access through Appearance > Editor.
Try it out and hope it helps.