Is it illegal for the property to disclose the owner's phone number?

Break the law. According to the provisions of the Property Law and the Civil Law, the personal information of residents belongs to private property that benefits from the sale of personal information, belongs to illegal income that benefits from the use of personal information, and belongs to infringement of personal rights.

Legal basis:

Article 253 of the Criminal Law Amendment of People's Republic of China (PRC): Staff of state organs and staff of financial, telecommunications, transportation, education, medical and other units. Whoever, in violation of state regulations, sells or illegally provides personal information of citizens obtained by the unit in the course of performing its duties or providing services to others, if the circumstances are serious, shall be sentenced to fixed-term imprisonment of not more than three years or criminal detention and shall also or only be fined.