A 62-year-old male smoker presents with a 3-month history of progressive hoarseness and throat pain. He has a 40 pack-year smoking history and occasional alcohol use. Laryngoscopy reveals a unilateral, irregular, ulcerated lesion on the left vocal cord with areas of necrosis. Biopsy confirms squamous cell carcinoma. CT neck shows the lesion confined to the vocal cord with no involvement of the anterior commissure, subglottis, or lymph nodes. According to the TNM staging system, what is the T stage of this tumor?