Prior research indicates that many people wish to limit aspects of their smartphone use. Why is it that certain smartphone use feels so meaningless? We examined this question by using interviews, the experience sampling method, and mobile logging of 86,402 sessions of app use. One motivation for use (habitual use to pass the time) and two types of use (entertainment and passive social media) were associated with a lower sense of meaningfulness. In interviews, participants reported feeling a loss of autonomy when using their phone in these ways. These reports were corroborated by experience sampling data showing that motivation to achieve a specific purpose declined over the course of app use, particularly for passive social media and entertainment usage. In interviews, participants pointed out that even when smartphone use itself was meaningless, it could sometimes still be meaningful in the context of broader life as a 'micro escape' from negative situations. We discuss implications for how mobile apps can be used and designed to reduce meaningless experiences.