For each phone, show its names and total number of stocks.
SELECT T2.Name ,  sum(T1.Num_of_stock) FROM phone_market AS T1 JOIN phone AS T2 ON T1.Phone_ID  =  T2.Phone_ID GROUP BY T2.Name
For each phone = GROUP BY phone name; total number of stocks = SUM(Num_of_stock); show its names = SELECT phone name;