As of Thursday June 8, 2023 the ChatGPT iOS app can be used on iPhone and iPad devices.
See ChatGPT iOS app - Siri and Shortcuts for an example walkthrough of using a combination of Siri and Shortcuts with the ChatGPT iOS app.
iPhone and iPad are both supported for the ChatGPT iOS app
As of Thursday June 8, 2023 the ChatGPT iOS app can be used on iPhone and iPad devices.
See ChatGPT iOS app - Siri and Shortcuts for an example walkthrough of using a combination of Siri and Shortcuts with the ChatGPT iOS app.