The speaker is watching someone close to them disappear into a phone, though the poem never names the device. The first lines list what is missing: tone, words, feeling, gesture. Nothing the speaker would normally rely on to connect with another person is there. The screen has taken it all, and the person is "hypnotized" and "addicted to the immediacy."
The mood turns from frustration to something sadder. When the speaker calls the person's name, they look up with a "deer-in-the-headlights stare," as if real conversation has become frightening. The person seems awkward, uncomfortable, and wishes the speaker would just leave. The short, clipped lines feel a little like text messages, which suits the title's idea of emotion being shortened to fit a screen.
The last line delivers the sting. The person has become "emotionless," just like the device they hold. The speaker sounds hurt, lonely, and quietly accusing.