I’d guess phone, anything else is too compute-constrained and just an accessory for them, plus has to pay 30% of subscriptions and can be disadvantaged strategically.
Likely a device where the largest share of interaction pattern is through voice conversations and chats with the system to get it to do things for you: messages, email, etc.
It would have to run Android, and try to provide compatibility for existing apps in order for this to be a successful device.
I don't really know, but from what I've heard it sounded kind of like a wearable amazon echo. Because I guess reaching into your pocket for your cell phone is too big a lift? Kind of fits with OpenAI's MO of only selling things that lose money (AFAIK the Echo is still unprofitable?)