Police said they have recovered a suicide note from the house in which the boy identified as Tarun has said that he was depressed over the episode.
The incident came to light around 6pm when Tarun's parents informed the police about the suicide. They claimed that the boy did not speak to anyone when he had come back home from the school on Saturday and had kept to himself.
In the note, the boy had claimed that he had tried to convince the teacher to give him back the mobile phone but he refused and asked him to meet with his parents on Monday.
Police said that Tarun studied in class 10 at a government school in east Delhi and his body has been sent for an autopsy at Lal Bahadur Shastri Hospital.
A case could be registered against the teacher in this regard after questioning, a police officer said.