I don't use a cell phone so I don't know about printing via the app.

If you log into your reservation on the website click on "Show more" on that sidebar on the left side. From there you can select "Print trip and receipt". That's always there even if you only see "Print trip" at the bottom of the reservation.

I just resize my margins (to .50 on the left & .25 for the rest. I set it to 73% & it fits on one page.