DECLARE @StartDate DATETIME
DECLARE @EndDate DATETIME
SET @StartDate = '1/1/2017'
SET @EndDate = '4/1/2017'
SELECT Demographics.PatientID, [Last] as LastName, [First] as FirstName, Gender, BirthDate, Phone FROM Demographics INNER JOIN
(SELECT DISTINCT PatientID FROM Billing WHERE DateOfService BETWEEN @StartDate AND @EndDate) as a on Demographics.PatientID = a.PatientID
WHERE phone is null or phone = ''
ORDER BY LastName