Is it possible that there was a simple misunderstanding during the phone call? They may have meant that you should save the PDF on your phone and carry that with you until such time as you were in a location where you could then print the boarding pass.

While I sympathise with you, Ryanair make absolutely no secret of the fact that they charge a punitive fee for having boarding passes issued at the airport - and further that the boarding passes have to be presented on paper, printed one-sided, and clearly legible. You should never (in any instance) rely on an undocumented oral assurance when all the written evidence clearly states the opposite.