The disposal of used smartphones has become an increasingly severe environmental problem, which are not only huge in quantities, but also contain harmful elements and scarce resources. There is an urgent need for effective management strategies to reduce the potential smartphones’ environment impacts. A new Life Cycle Assessment (LCA) model, covering five phases of “production, transportation, distribution, usage and recycling” was constructed for quantification of the carbon footprint 5G smartphones. Based on the usage and recycling scenarios of 5G smartphones taken by the youth, adult and elderly users in China, the results of carbon footprints of smartphones from cradle to cradle were compared, which depend more on recycling pattern. Repurposing of smartphone is the best way to reduce the environmental impact. and secondly use of replacement parts can bring a certain carbon offset, while leaving the used devices idle are the worst. Results of the analysis reveal that functional transformation and reuse represents a strategic choice of circular economy with more environmental advantages. Recycling pattern and the reuse ratio of disassembled parts determine the carbon footprint of smartphones, and promoting the repurposing of used devices within the household is much more helpful to improve the carbon footprint of smartphones.