Try something like:
CREATE PROC [dbo].[InsertPhone]
@EmployeeNo int
AS
BEGIN
DECLARE @CONTEXT_INFO varchar(100)
DECLARE @PhoneNo varchar(15)
SELECT @CONTEXT_INFO = COALESCE(CONVERT(VARCHAR(128), CONTEXT_INFO()), CURRENT_USER)
SELECT
@PhoneNo = Ad.PhoneNo
FROM
User Ad
WHERE Ad.Employeeno= @EmployeeNo
INSERT INTO [Phone]
(employeeno, PhoneNumber, CreatedBy, UpdatedBy)
VALUES
(@EmployeeNo, @PhoneNo, @CONTEXT_INFO, @CONTEXT_INFO)
END
Now, if you need some modifications on exists or not (that would need a if and then UPDATE/INSERT staments), then make the changes accordingly.
Try!