MySQL getting result using 3 Tables and case statements
MySQL does not support full outer joins, so you will have to use unions:

select phno,
if(count(phno1) = 0, 'No', 'Yes') as person,
if(count(phno2) = 0, 'No', 'Yes') as person2,
if(count(phno3) = 0, 'No', 'Yes') as person3,
from (select phno, phno as phno1, NULL as phno2 , NULL as phno3 from person  
      union
      select phno, NULL as phno1, phno as phno2 , NULL as phno3 from person2   
      union
      select phno, NULL as phno1, NULL as phno2 , phno as phno3 from person3
) sub
group by phno


If you only want to check for a single person, you can use Aditys code slight modifications:

SELECT DISTINCT p.phno AS 'phno',
(CASE WHEN ISNULL(person.phno) THEN 'NO' ELSE 'Yes' END) AS 'person',
(CASE WHEN ISNULL(person2.phno) THEN 'NO' ELSE 'Yes' END) AS 'person2',
(CASE WHEN ISNULL(person3.phno) THEN 'NO' ELSE 'Yes' END ) AS 'person3'
FROM (SELECT 4567 AS phno) p
LEFT JOIN person ON p.phno = person.phno
LEFT JOIN person2 ON p.phno = person2.phno
LEFT JOIN person3 ON p.phno = person3.phno;


It does work, I just tested it myself, feel free to execute my test and confirm:

DROP TABLE IF EXISTS person;
CREATE TABLE person(NAME VARCHAR(255), phno INT);
DROP TABLE IF EXISTS person2;
CREATE TABLE person2(NAME VARCHAR(255), phno INT);
DROP TABLE IF EXISTS person3;
CREATE TABLE person3(NAME VARCHAR(255), phno INT);

INSERT INTO person(NAME, phno)
VALUES ('abc', 1234),('def', 2345),('ghi', 3456),('jkl', NULL);

INSERT INTO person2(NAME, phno)
VALUES ('abc', 1234),('def', 2345),('ghi', NULL),('jkl', 4567);

INSERT INTO person3(NAME, phno)
VALUES ('abc', NULL),('def', 2345),('ghi', 3456),('jkl', 4567);

SELECT DISTINCT p.phno AS 'phno',
(CASE WHEN ISNULL(person.phno) THEN 'NO' ELSE 'Yes' END) AS 'person',
(CASE WHEN ISNULL(person2.phno) THEN 'NO' ELSE 'Yes' END) AS 'person2',
(CASE WHEN ISNULL(person3.phno) THEN 'NO' ELSE 'Yes' END ) AS 'person3'
FROM (SELECT 4567 AS phno) p
LEFT JOIN person ON p.phno = person.phno
LEFT JOIN person2 ON p.phno = person2.phno
LEFT JOIN person3 ON p.phno = person3.phno;


result:

phno  person  person2  person3
4567  NO      Yes      Yes