Previous studies show that infants store functional morphemes for inferring syntactic categories of adjacent words, and they generally perform better with nouns than with verbs. In this study, we tested whether toddlers can exploit phrasal groupings for syntactic categorization in the face of noisy co-occurrence patterns. Using a visual fixation procedure, we examined whether Mandarin-learning 19-month-olds can categorize word X to the left of functional morpheme a in a prosody-neutral 3-word sequence X-"a"-Y, where a structurally selects X (X and Y being unfamiliar words). Infants at 19 months were familiarized either with X-"ye"-Y ('even X[subscript N] Y[subscript V]') or with X-"le"-Y ('have X[subscript V]-ed Y[subscript N]'). While le features a more mixed distribution than "ye," 19-month-olds succeeded with both "ye" and "le" by preferring grammatical new contexts of X over ungrammatical ones, consistent with the hypothesis that phrasal groupings ([Xa. . .]) support syntactic categorization. Our findings provide initial evidence for infants' ability to capture functional morphemes for backward syntactic categorization.