Phenyl amine is the weakest base- the benzene group has a negative inductive effect on the lone pair on the nitrogen. Therefore it is less availiable for donation.
Methyl amine is the strongest- the methyl group has a positive inductive effect on the lone pair on the nitrogen. Therefore it is more avaliable for donation.
Methylphenyl amine is in the middle as these 2 groups are both attatched to the nitrogen so the inductive effects work in opposition