Sorry for the unnecessary post. I just noticed that this exact same issue was addressed in a previous post. I must have not used the right search terms when I searched the forum.
Sorry it took so long to get back to you. I tried the CSS that you posted and still got one column on my phone. Below is a link to screenshots of the Gallery editing page showing my settings and the result on my phone. I tried setting the “gutter” to both 20 and 40 and got the same result.
