The ubiquitous presence of smartphones raises significant concerns regarding their impact on users' digital well-being. This study delves into the complex relationship between smartphone usage patterns and digital wellbeing while focusing on the physical, intellectual, mental and social dimensions of well-being. We examine the smartphone usage behaviors of university students over a span of two weeks, by logging smartphone usage data and simultaneously sampling users' perceived experiences. Drawing upon data from 48 university students, we reveal that digital wellbeing is intricately connected to the how, when, and why of smartphone usage. App-switching behavior and the diversity of individualized usage patterns play pivotal roles in shaping the digital wellbeing landscape. Additionally, the promotion of intentionality in smartphone interactions emerges as a critical strategy for enhancing digital wellbeing. These findings underscore the need for personalized interventions to enhance digital wellbeing in an era dominated by digital technology.