The use of vitamin D to reduce the severity of COVID-19 complications is receiving considerable attention, backed by encouraging data. Its purported mode of action is as an immune modulator. Vitamin D, however, also affects metabolism of phosphate and Mg, which may well play a critical role in SARS-CoV-2 pathogenesis. SARS-CoV-2 may induce a cytokine storm that drains ATP whose regeneration requires phosphate and Mg. These minerals, however, are often deficient in conditions that predispose people to severe COVID-19, including older age (especially males), diabetes, obesity, and usage of diuretics. Symptoms observed in severe COVID-19 also fit well with those seen in classical hypophosphatemia and hypomagnesemia, such as thrombocytopenia, coagulopathy, dysfunction of liver and kidneys, neurologic disturbances, immunodeficiency, failure of heart and lungs, delayed weaning from a respirator, cardiac arrhythmia, seizures, and finally multi-organ failure. Deficiencies of phosphate and Mg can be amplified by kidney problems commonly observed in COVID-19 patients resulting in their wastage into urine. Available data show that phosphate and Mg are deficient in COVID-19 with phosphate showing a remarkable correlation with its severity. In one experiment, COVID-19 patients were supplemented with a cocktail of vitamin D3, Mg, and vitamin B12, with very encouraging results. We thus argue that COVID-19 patients should be monitored and treated for phosphate and Mg deficiencies, ideally already in the early phases of infection. Supplementation of phosphate and Mg combined with vitamin D could also be implemented as a preventative strategy in populations at risk.