How do I change the number of columns on mobile?

The Visual Portfolio block reduces columns automatically. A 3-column Masonry, Grid or Tiles gallery shows 2 columns at 768 px and below and 1 column at 576 px and below; a 5-column one shows 4 at 1200, 3 at 992, 2 at 768 and 1 at 576. Pro users can move these widths in Settings → General → Responsive Breakpoints.

To keep two columns on phones, add to the block’s Custom CSS:

@media screen and (max-width: 576px) {
	selector .vp-portfolio__item-wrap {
		width: 50% !important;
	}
}

Justified and Slider have no column width to override. Slider steps down its slides per view the same way.

See Custom CSS. The full column ladder is on Responsive behaviour.