Does basic 2 PL always ensure conflict serializability? While going through the DBMS book by Korth, it was mentioned : 

" For a set of transactions, there may be conflict-serializable schedules that
cannot be obtained through the two-phase locking protocol.

Does this imply that basic 2 PL ensures serializability but does not always ensure conflict serializability ?
No,

If you use 2PL protocol you are guaranteed to have a conflict-serializable schedule but there are conflict serializable schedules which may not honour 2 PL protocol i.e. locking data items in the growing phase and releasing them in the shrinking phase.