Background: Patients with COVID-19 may develop several electrolyte imbalances that can cause multiple clinical complications. Low serum phosphorous level usually leads to a decreased muscle ATP synthesis which may cause diaphragmatic or other kinds of respiratory muscle weakness. We investigated the predictive power of serum phosphorus levels in patients with hospitalized COVID-19. Material and Methods: This is a retrospective and observational study of 957 patients with SARS-CoV-2, who were diagnosed with COVID-19 by real-time PCR testing and hospitalized due to moderate and severe COVID-19 pneumonia. Results: Among 957 patients with COVID-19 pneumonia, 387 (40,4%) were moderate and 570 (59,6%) were severe. Phosphorus was significantly lower in severe patients, within the reference range. Our final analysis showed that age, respiratory rate, d-dimer, and phosphorus level were independent risk factors for disease severity. Phosphorus was found to be negative correlated with respiratory rate (r: 0,091, p=0,005) and was positive correlated with SPO2 (r: 0,069, p=0,03). Conclusion: Our results suggest prognostic significance of phosphorus level, which has correlation with the respiratory rate and has considered to be independent risk factor for disease status, especially in severe patients. It is concluded that phosphorus monitoring, at least in severe patients, may prevent serious clinical consequences such as respiratory insufficiency. Keyword; COVID-19, pneumonia, phosphorus, respiratory muscle, disease status, predictive value