public class GroupMember {
private String role;
private String name;
private String phoneNumber;

@PropertyName("phone_number")
public String getPhone() {
    return phoneNumber;
}

@PropertyName("phone_number")
public void setPhone(String phone) {
    this.phoneNumber = phone;
}

@PropertyName("role")
public String getRole() {
    return role;
}

@PropertyName("role")
public void setRole(String role) {
    this.role = role;
}

@PropertyName("name")
public String getName() {
    return name;
}

@PropertyName("name")
public void setName(String name) {
    this.name = name;
}
}

public class GroupMember {
private String role;
private String name;
private String phone_number;

public String getPhone() {
    return phone_number;
}

public void setPhone(String phone_number) {
    this.phone_number = phone_number;
}

public String getRole() {
    return role;
}

public void setRole(String role) {
    this.role = role;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}
}

Map<String, Object> map = (Map<String, Object>) dataSnapshot.getValue();
String phone = (String) map.get("phone_number");
String name = (String) map.get("name");