pK_b tells the strength of a base. Lower is pK_b value, stronger is the base. Now C₆H₅NH₂ is a weak base because the lone pair is involved in resonance with the benzene and is thus not available for a donation while in C₂H₅NH₂, C₂H₅ is an electron donating group, which increases the e- density on N thus felicitating the release of lone pair. Hence, C₂H₅NH₂ is a strong base.
Thus, the correct order is:

C₂H₅NH₂< C₆H₅NHCH₃< C₆H₅NH₂