Within the existing script would be fine. Subflows are more useful when you have large chunks of code (e.g. account entry and validation against a database) that you wish to reuse across multiple scripts.
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Create Generated Prompt - The value from the statistics step, ordinal type.
Play Prompt - P[prefix.wav] + P[generated.wav] + P[suffix.wav]
Please remember to rate helpful responses and identify helpful or correct answers.