Phosphate is a predominately intracellular anion that has several key roles in normal cellular functions. Derangements in serum phosphate concentration occur frequently during critical illness, particularly hypophosphataemia, which has been reported in up to 75% of Intensive Care Unit (ICU) patients. The association between hypophosphataemia and ICU outcomes reported in the literature are conflicting and and subject to substantial confounding. Exogenous phosphate can be administered in the ICU using the enteral and intravenous route safely. However, whether administering phosphate and correcting hypophosphataemia results in any patient-centred benefits, or harms, remains uncertain, particularly for patients with mild hypophosphataemia or low-normal phosphate levels. This review will highlight key aspects of hypophosphataemia management in the critically ill, summarise current best practice, and outline major research priorities.