The one-column format is fine on a large monitor, but on a small phone I prefer narrower columns, because a wide column would either make the text too small or it would require horizontal panning while reading.
So I consider the two-column format as better for phones, not worse.
The usual two-column layout is because having 40 to 60 characters per line in a single column is wasteful of paper. That is a real issue. But the solution is to make the PDF page narrower. Almost nobody prints these documents anyways; there's no good reason they need to conform to legacy sizes like A4 or letter paper commonly found in office printers. Just choose A5 as the size. People who really need to print can fit two A5 pages on one A4 page, and people who view these documents on a phone screen will also find A5 more convenient.