A customer of mine wants to have different check-out process based on device. They would like the ecom80, single page checkout on mobile and the ecom90 (multiple step checkout) on desktop.
I have not tested it, but on the page with your checkout flow, there are 2 paragraphs - only one active. See dump #1.
Activate both of them. Then set the "Accessibility" options on both of them - hide multistep for phones, and onstep for tablets and desktops. See dump 2 and 3.