CREATE TABLE author(
author_id INT AUTO_INCREMENT PRIMARY KEY,
name VARCHAR(20),
author_phone_fk INT NULL,
CONSTRAINT  `author_phone_fk`
FOREIGN KEY(author_phone_fk) REFERENCES phone(phone_id));

CREATE TABLE phone(
phone_id INT AUTO_INCREMENT PRIMARY KEY,
number VARCHAR(20));

@Entity
public class Phone {

    @Id
    @Column(name = "phone_id")
    private int id;

    private String number;

  }

@Entity
public class Author {

    @Id
    @Column(name = "author_id")
    private int id;

    private String name;

    @OneToOne(cascade = CascadeType.PERSIST)
    @JoinColumn(name = "author_phone_fk")
    private Phone phone;
}