Kwok,
Please use this custom css and it should fix your issue.
Please use this css. It should allow 1 column in mobile devices.
@media only screen and (max-width: 480px) and (min-width: 321px) {
.wmle_container.responsive .wmle_item_holder.col5{width:100%}
.wmle_container.responsive .wmle_item_holder.col4{width:100%}
.wmle_container.responsive .wmle_item_holder.col3{width:100%}
.wmle_container.responsive .wmle_item_holder.col2{width:100%}
}
Hope this helps.
Thanks