Hypophosphatemia is a frequent complication of chimeric antigen receptor T-cell therapy. In this setting, hypophosphatemia has been previously associated with cytokine release syndrome. The mechanisms underlying this electrolyte derangement are not fully understood. Extracellular phosphate consumption by chimeric antigen receptor T-cells was demonstrated in vitro, but inflammation is also thought to play a contributing role. We present a case of severe, refractory hypophosphatemia with renal phosphate wasting triggered by hemophagocytic lymphohistiocytosis in acute lymphoblastic leukemia.