Postnasal Drip: This condition occurs when excess mucus from the nose drips down the back of the throat, causing phlegm and a hoarsed voice, especially at night when lying down. The symptoms improve in the morning as the mucus is cleared.

Acid Reflux (Gastroesophageal Reflux Disease, GERD): Stomach acid can flow up into the throat at night, causing irritation and leading to phlegm production and a hoarsed voice. Symptoms often improve in the morning.
Allergic Rhinitis: Allergies can cause increased mucus production, leading to phlegm, especially at night. A hoarsed voice can result from the constant clearing of the throat.
Sinusitis: Inflammation of the sinuses can lead to increased mucus production, which may worsen at night and improve in the morning as the body clears out the mucus.

Laryngopharyngeal Reflux: A more severe form of acid reflux that specifically affects the larynx and pharynx, potentially causing significant voice changes and phlegm.
Thyroid Disorders: Certain thyroid conditions can affect the voice and cause phlegm, though this is less common.
Tuberculosis or Other Chronic Infections: Though rare, chronic infections can cause persistent phlegm and voice changes, and it's crucial not to miss these diagnoses due to their serious implications.

Vocal Cord Lesions: Polyps, nodules, or cysts on the vocal cords can cause a hoarsed voice and potentially lead to phlegm production if there's associated inflammation or infection.
Sleep Apnea: While primarily known for causing pauses in breathing during sleep, sleep apnea can also lead to increased phlegm production due to the body's response to the lack of oxygen.
Cystic Fibrosis: A genetic disorder that leads to the production of thick, sticky mucus, which can cause phlegm and respiratory issues, though it's typically identified at a younger age.