The present invention can include a method for tuning grammar option weights of a phrase-based, automatic speech recognition (ASR) grammar, where the grammar option weights affect which entries within the grammar are matched to spoken utterances. The tuning can occur in an unsupervised fashion, meaning no special training session or manual transcription of data from an ASR session is needed. The method can include the step of selecting a phrase-based grammar to use in a communication session with a user wherein different phrase-based grammars can be selected for different users. Feedback of ASR phrase processing operations can be recorded during the communication session. Each ASR phrase processing operation can match a spoken utterance against at least one entry within the selected phrase-based grammar. At least one of the grammar option weights can be automatically adjusted based upon the feedback to improve accuracy of the phrase-based grammar.