"ChatGPT but a voice chat robot" is ChatGPT, but that feature is still in the process of being rolled out.
See ChatGPT can now see, hear, and speak for more information:
We’re rolling out voice and images in ChatGPT to Plus and Enterprise users over the next two weeks. Voice is coming on iOS and Android (opt-in in your settings) and images will be available on all platforms.
Speak with ChatGPT and have it talk back
You can now use voice to engage in a back-and-forth conversation with your assistant. Speak with it on the go, request a bedtime story for your family, or settle a dinner table debate.
To get started with voice, head to Settings → New Features on the mobile app and opt into voice conversations. Then, tap the headphone button located in the top-right corner of the home screen and choose your preferred voice out of five different voices.
The new voice capability is powered by a new text-to-speech model, capable of generating human-like audio from just text and a few seconds of sample speech. We collaborated with professional voice actors to create each of the voices. We also use Whisper, our open-source speech recognition system, to transcribe your spoken words into text.