Then you need to use an outer join
And to make it more readable you should avoid implicit joins, spell them out properly using ANSI joins.
Try this:
SELECT Booking_ID
,Book_Time
,a.Name as Driver
,b.Name as Commuter
,Distance as Estimated_Travel_Distance
,Price_Min
,Price_Max
,book.Distance_Travelled as Actual_Distance
,(Distance_Travelled *Basic_Fare) as Actual_Fare
FROM Booking_t book
JOIN locations_info_t loc
ON book.Distance_Travelled = loc.Distance
JOIN cartype_t ct
ON book.Car_Type = ct.Car_Type_Name
JOIN user_t b
ON book.Commuter = b.Phone_Num
left OUTER JOIN user_t a
ON book.Driver = a.Phone_Num
WHERE extract(month from Book_time) = 2
AND extract(year from Book_time) = 2014
AND extract(day from Book_time) < 16;
By the way, you need to use proper keys. If a driver changes his phone number his records in the booking table will have disappeared