Hi Croakie,
To clarify, the camera's Bluetooth capabilities will not allow a wireless connection with a smartphone or other wireless device. It's just a convenient way to go through the initial setup, The actual wireless communication is done through the Wi-Fi protocol, but you don't need wireless access to the internet to make it work. Instead the camera creates a network of sorts that certain devices, like smartphones, can join.
To set up a connection with your iPhone, I suggest that you reference the illustrated steps that start on page 176 of the PowerShot SX70 Advanced User Guide. I've included a link to that below:
http://gdlp01.c-wss.com/gds/1/0300032371/02/pssx70hs-ug2-en.pdf#page=176
If problems persist, please elaborate on what step causes issues for you.
