You will almost certainly have a working Fastboot mode so that you could move forward with the regular install method Install /e/OS on a Fairphone The Fairphone (Gen. 6) - “FP6” .
You might study one or two threads with hashtag eosinstaller . There is no documented way to get a log of the fail, so it is a pure guess but maybe the flashing procedure started but aborted silently.
Take a bit of time to familiarise with the install steps but don’t hesitate to ask about anything unclear.
Good luck.