The coronavirus 2019–2020 pandemic (COVID-19) poses unprecedented challenges for governments and societies around the world. Non-pharmaceutical interventions have proven to be critical for delaying and containing the COVID-19 pandemic. These include testing and tracing, bans on large gatherings, nonessential business and school and university closures, international and domestic mobility restrictions and physical isolation, and total lockdowns of regions and countries. Decision-making and evaluation or such interventions during all stages of the pandemic life cycle require specific, reliable, and timely data not only about infections but also about human behavior, especially mobility and physical co-presence. We argue that mobile phone data, when used properly and carefully, represents a critical arsenal of tools for supporting public health actions across early, middle, and late stage phases of the COVID-19 pandemic.