Yes (but read on). Texting, gaming, watching videos, scrolling on social media, etc. are all accepted. But of course, make sure to use earphones or headphones when listening to music or watching videos. You’re good to go as long as it doesn’t disturb others.
With that said, there are a couple of rules.
For example, calling is a definite no-go. If it’s an absolute emergency, you can move by the door and talk very quietly but it’s not ideal. Also, technically, you should turn off your phones around priority seats, which are reserved for people with disabilities and injured, pregnant, or elderly individuals as well as small children. The concern is that the radio waves emitted by mobile devices may disrupt those who may have pacemakers. Although I’ve never seen anyone actually follow this rule (especially because it can only make a difference if the phone is 15 centimeters or less from the implanted medical device), it would be a very considerate gesture.
Learn more about train etiquette in Japan: https://www.jrailpass.com/blog/japan-train-etiquette