App Store on iOS 17.1.1 in Europe has ChatGPT app version 1.2023.319 (14269) released three days ago. No sign of ChatGPT Voice. No headphone icon to be found. There’s also no «New Features» entry in Settings on the mobile app and so no way to opt into voice conversations as the blog article suggests. https://openai.com/blog/chatgpt-can-now-see-hear-and-speak

Edit: The headphone icon appeared on Nov 22, 2023 around 6am CET without an update to the app. There is no «New Features» entry in the Settings.