FOUND A SOLUTION BY MYSELF AND WANT TO SHARE IT WITH YOU GUYS! So to be honest I totally gave up on this issue and accepted the fact that all my photos are lost. But as a last possibility I opened up the phone, disconnected the sensor/earpiece flex cable and connected the phone to my Mac. Again iTunes told me that the phone had to be restored/updated in order to work again. So I hit the "Update" button and BOOOOOM it successfully installed iOS 11.4 and my phone came back to life.