I am missing ‘say phone to tether’. Plug US in the phone, open the drop-down menu (slide the finger from very top down). There is something with ‘USB charging, click for more’. There are different options ‘Charging, Filetransfer, MTP, PTP, … , Tethering’.

If this option won’t appear when connected to the Flint, does it appear while connected to a PC/Laptop/Notebook/…? Read your text twice. Maybe my first suggestion is not relevant, too …