Disclosed herein are FGF23 c-tail fusion proteins, pharmaceutical compositions comprising the FGF23 c-tail fusion proteins, and methods of treatment using the FGF23 c-tail fusion proteins. This application discloses fusion proteins comprising a FGF-23 c-tail protein fused to a heterologous amino acid sequence, wherein said fusion protein modulates serum phosphate levels but does not substantially modulate serum 1, 25 VitD levels. In some embodiments, the FGF-23 c-tail protein is fused to the heterologous amino acid sequence via a linker. This invention also encompasses vectors comprising the nucleic acids disclosed herein, and a host cell comprising the vector or polynucleotides encoding the proteins of the invention.