You are designing two Microsoft Copilot Studio agents named Agent1 and Agent2.

Agent 1 = NLU

Agent 2 = NLU and NLU+

https://learn.microsoft.com/en-us/microsoft-copilot-studio/nlu-overview

Agent1 must support simple and short phrases for a given topic . That is the classic use case for NLU in Copilot Studio. NLU is designed for standard intent recognition where users enter brief, predictable utterances tied to a topic.

This makes NLU the best fit for:

narrow topic triggering

short phrase matching

standard, non-generative agent behavior

Why Agent2 = NLU+

Agent2 must integrate with Microsoft Dynamics 365 Contact Center voice channel . For that scenario, NLU+ is the correct recommendation among the listed standard models.

NLU+ extends the standard NLU approach and is the model aligned to scenarios that need stronger language understanding support in more advanced enterprise channel integrations such as voice experiences. Since the requirement explicitly says:

use a standard model

do not use generative orchestration

NLU+ fits better than Azure OpenAI or other generative options.