Phosphorus is a resource that is utilized with efficiency in most parts of the world. Farmers fertilize with increasing precision; wastewater treatment plants strip phosphorus from sewage; and industries make use of phosphorus byproducts. Why, then, do incidents of eutrophication and harmful algal blooms related to excessive phosphorus outflows continue to intensify? Incremental improvements in phosphorus use efficiency and monitoring of individual phosphorus waste streams no longer seem sufficient to dampen these environmental impacts. A radical shift in perspective is needed, one in which phosphorus is treated as a resource rather than as waste. Using substance flow analysis, we explore various types of phosphorus management scenarios for a specific system, for the urban city-state of Singapore. These scenarios are jointly framed with the urban planning agency of Singapore and takes into consideration both behavioral and infrastructural changes to the status quo. These scenarios include strategies and technologies such as composting, separated incineration of organic and non-organic waste, anaerobic co-digestion of food waste and wastewater, and dedicated anaerobic digestion of food waste and wastewater. Publicly available UN Comtrade data is used to establish temporal trends in phosphorus consumption between 1989 and 2012. Phosphorus waste outputs are verified via empirically collected data on household and commercial waste generation. The results of this paper demonstrate how the transition from a linear to a closed-loop phosphorus cycle might be possible for Singapore, an island that is an important test bed for planning the sustainable metabolism of future urban areas.