To use your iPhone’s internet connection through a Linux notebook over bluetooth, you have to open Tethering option on your iPhone device, under the Settings->General->Network section.
After that you can install Blueman (a simple and intuitive bluetooth manager) for easily configuring bluetooth PAN network:
apt-get install blueman
Start blueman-manager and find your mobile device and connect to it. When connection completed successfully, select Device->Add->Network Access Point in blueman-manager.
And the last step, configure the network interface: