1. A method comprising: receiving a speaker identity claim (SIC) utterance; recognizing the SIC utterance; extracting at least one voice characteristic from the SIC utterance and comparing same with a voice profile registered under the SIC in a voice profile database to generate a first score; making a first verification decision based on the first score; generating and prompting a user to speak a first dynamic phrase (FDP); receiving an FDP utterance; extracting at least one voice characteristic from the FDP utterance and comparing same with the voice profile registered under the SIC in the voice profile database to generate a second score; making a second verification decision based on the second score; if the second verification decision indicates a low confidence level, rejecting the speaker identity claim; if the second verification decision indicates a high confidence level, accepting the speaker identity claim; and if the verification decision indicates a medium confidence level: generating and prompting the user to speak a second dynamic phrase (SDP); receiving an SDP utterance; extracting at least one voice characteristic from the SDP utterance and comparing same with the voice profile registered under the SIC in the voice profile database to generate a third score; and making a third verification decision based on the third score.