Nosebleeds, tuberculosis, cystic fibrosis and bronchitis are some causes of blood in phlegm. Other causes include laryngitis, dehydration, aspiration pneumonia and trauma, according to Healthline.
Coughing up bloody phlegm, also known as hemoptysis, is also caused by blood clots in the lungs, throat irritation and lung cancer, claims UCLA. Cough medicine is usually a first-line treatment for hemoptysis, claims MedlinePlus. It is recommended to keep track of how much blood is mixed in the phlegm and how long the cough lasts. If there are more than a few teaspoons of blood in the phlegm, or if it comes with symptoms such as chest pain, dizziness, fever and shortness of breath, medical attention is required.