We had previously learned that nhà báo means journalist. Is there a difference between these two terms in Vietnamese? Is one more frequently used?
yes, there is a difference in VNmese. "nhà báo" is normally used to refer to the person who collects news and writes for a written press. "phóng viên", literally an interviewer, is more used in reference to a person reporting news over a television or radio newscast.
Perhaps we need to differentiate these two professions in English and apply it to Vietnamese. A journalist gathers news and is part of the editorial process. You and me could be reporters, ones who forward the news to be considered for dissemination.
Nhà báo are journalists. Reporters are phống viên. I remember it by "nhà" also word for house, where the gathered news comes in for editorial work. House is "bigger".