SELECT IFNULL(C.agentDisplayPhone,IFNULL(B.phone,a.agentphone))  as agentphone
FROM agents AS a 
Left Outer Join agents_geoposition B On B.id = a.id
Left Outer Join agentsPhones C On C.agentid = a.id And LENGTH(C.agentDisplayPhone) > 1 And C.agentPhone = IFNULL(B.phone,a.agentphone) WHERE a.id = <br>