In this case, the patient's intact FGF-23 level of 92 pg/mL exceeded the adjusted TIO cutoff by approximately 1.35-fold (mild elevation) and the XLH cutoff by over fourfold (moderate elevation), signifying pathological FGF-23 overproduction; this elevation, combined with persistent hypophosphatemia, renal phosphate wasting, inappropriately low-normal 1,25 Vit D, negative genetic testing, and rapid symptom resolution with burosumab (an FGF-23 inhibitor), compellingly supports an FGF-23-mediated phosphaturic disorder such as TIO, despite the elusive tumor on imaging. Here, FGF23 is linked to hypophosphatemia.