The iPhone uses the MFI to connect to hearing aids. I don’t think even the iPhone 14 has BT LE Audio yet. It’s not clear if the iPhone 15 will have it at this point.
When you use the iPhone for phone calls with hearing aids, the mic on the iPhone is still used to pick up your voice with the MFI connection. So if you put your iPhone in your pocket or not near your mouth, the mic from the iPhone will not be able to pick up your voice clearly.