Yes, it is considered extremely rude and a significant breach of social etiquette to talk on the phone while riding a bus or train in Japan. Japanese public transit is governed by the concept of meiwaku, which translates to avoiding being a nuisance to others. Passengers are expected to switch their phones to "manner mode" (silent) and refrain from making or receiving calls to maintain a quiet, peaceful environment for everyone. If your phone rings, the standard practice is to quickly silence it or decline the call; if you must answer, you should do so in a whisper only to say "I'm on the bus, I'll call you back," and then hang up immediately. This cultural norm is so strong that most vehicles have signs and frequent bilingual announcements explicitly asking passengers to refrain from voice calls. While texting or using apps silently is perfectly acceptable, verbal conversations are viewed as intrusive and disrespectful to the collective space of the other commuters.