Disclosed herein are methods, systems, and apparatus, including computer programs encoded on computer storage media, for phone fraud prevention. One of the methods includes adding a first identifier of a first phone event of a first user into a blockchain managed by one or more devices on a decentralized network. The first identifier of the first phone event is classified into a list of phone fraud identifiers. A second identifier of a second phone event involving a second user is received. The second identifier is compared with the list of phone fraud identifiers that includes the first identifier. In a case where the second identifier matches a phone fraud identifier in the list of phone fraud identifiers, the first user is notified that the second phone event involves a risk of phone fraud.