Yeah, i am following the instructions from that page. and there it is stated, that i shall do the following:
Type
adb devices
and press Enter. You will see a pop-up on your Fairphone asking if you allow USB debugging on this computer. Tap **Allow
Next, type
adb reboot bootloader
and press Enter. The phone will now reboot into fastboot mode.**.
While in fastboot mode, type
fastboot flashing unlock
and press Enter. Follow the instructions that appear on your Fairphone’s screen. This action will wipe all the personal data on your phone.
I can enter the fastboot mode using Vol Down + Power, but i cannot use fastboot as it seems. It states:
./fastboot flashing unlock
< waiting for any device >
I will try to bring my adb key to the phone via sd card. That might help.