When adding rows & columns to your email design, you can add up to 5 Columns in a single row side by side. When viewed on a smaller mobile screen, these columns will stack on top of each other. Try choosing the 2 bottom column layouts highlighted below for different layout options.
On smaller screens the 2 side-by-side columns will stack on top of each other, and the smaller column will always sit on top. So for example in a newsletter format, you can experiment with alternating layouts; an image on the left and text paragraph on the right, and vice versa.
Using these options will allow you to keep your layout format consistent when viewed on a mobile device.
In the gif animation below, you can see these stacking columns in action. In the first row, the 'blue 1' section on the left stacks on top, and in the second row it's the opposite, the 'pink 2' section stacks on top.
So select either one of the bottom 2-Column options to get the layout that works best for your email design.