-- OrtizOL - xCSw - http://ortizol.blogspot.com

SELECT c.CustomerID,
    SalesPersonPhone = spp.PhoneNumber,
    CustomerPhone = pp.PhoneNumber,
    PhoneNumber = COALESCE(pp.PhoneNumber, spp.PhoneNumber, 'SIN TELÉFONO')
FROM Sales.Customer c
    LEFT OUTER JOIN Sales.Store s
        ON c.StoreID = s.BusinessEntityID
    LEFT OUTER JOIN Person.PersonPhone spp
        ON s.SalesPersonID = spp.BusinessEntityID
    LEFT OUTER JOIN Person.PersonPhone pp
        ON c.CustomerID = pp.BusinessEntityID
ORDER BY CustomerID;