ok, i found it 
i needed to add my phone ID to ~/.android/adb_usb.ini
(see here – unfortunately only in german)
–> find it via “lsusb” (run it, disconnect the phone, run it again – you see which ID is missing, that was the phone ;))
add “0x” + the first 4 characters of the ID (before the colon)
so, e.g. “0x1234” to the file (create it if it does not exist)