An approach to synthesize monodisperse nanospheres with nanoporous structure through a solvent extraction route using an acid–base-coupled extractant has been developed. The nanospheres form through self-assembly and templating by reverse micelles in the organic solvent extraction systems. More importantly, the used extractant in this route can be recycled. The power of this approach is demonstrated by the synthesis of monodisperse iron phosphate nanospheres, exhibiting promising applications in energy storage. The synthetic parameters have been optimized. Based on this, a possible formation mechanism is also proposed. The synthetic procedure is relatively simple and could be extended to synthesize other water-insoluble inorganic metal salts.