As a gate agent, we help lots of customers every day. Travelers like to have their boarding pass on their phone. As an agent, it is difficult to assist you without having a printed boarding pass.
Anytime you ask question, we need the information on that boarding pass, including your name, flight, reservation code, seat number. If it is on your phone, we have a difficult time to see that. We do not like to take possession of your phone.
So next time you are traveling. Please, if you can, get a hard copy of that Boarding Pass!