The OTA updater (http://ota.fairphone.com/FP2/updater.zip) points to this file:
http://storage.googleapis.com/fairphone-updates/FP2-gms36-1.1.7-ota.zip
Does this help?
EDIT: Sorry, I just realized that this only contains boot.img - I doubt this is sufficient to rebuild the complete system. 
Well what I did was simply a hard reset. That got me so far that I could boot up the phone again, so - to undo the rest of the damage I did - I could reinstall the OS through the updater App.
Okay,
where would I get the proper system.img to flash it to the phone? Another user was so kind to send me his build of the FP2-osos, but if I try to flash it via adb sideload I get:
Finding update package…
Opening update package…
E:footer is wrong
E:signature verification failed
Installation aborted
So something seems not to be right…
The .zip file contains the file system.new.dat. Apparently you can convert it to a system.img like this:
Good luck, trying…
Is this really needed? I think the device should be able just use FP2-gms36-1.1.7-ota.zip (on a SD/sideloaded) from the recovery. But I don’t have a FP2 so I don’t want to say anything wrong.
It actually did work!
It just took me some time downloading the package but flashing works as it is and I didn’t need to convert anything. Phone took something like 5 minutes to boot afterwards (probably running after-installation and setup scripts) but now it’s very vanilla again!
Thanks for the link to the ota-update @root and thanks for the support @USB-2 
Cool!
It’s a seriously important thing we learnded here today! 
It think the is currently a lot of confusing info floating around (What does the recovery verify?, what’s inside the ota? Does a full backup work? Shameless plug: I think the best source for info right now is the wiki here, if one does not want to read all the threads in the forum. 
So, how did you actually do it? Copy the .zip to an SD card, boot the recovery and use “apply update from sdcard”? I’m currently trying to send the .zip via sideload but when the PC is at ~40% the phone cancels the process:
Finding update package…
Opening update package…
Verifying update package…
E:failed to verify whole-file signature
E:signature verification failed
I verified the MD5 of the ota-zip with the one from the updater.xml and they match.
Is there a file size limit for sideload? I’d need to find a free µSD-card to test the “from sdcard”-approach.
UPDATE: Found a suitable µSD-card and I’m currently copying the OTA zip file to it
Did it work? If the checksum matches, you should be able to sideload the .zip from the SD card. I hope it will work for you!
Nope, sideloading the OTA-zip doesn’t work for me. I also tried different USB-cables. It might fail since the recovery I’m using is self-compiled using the instructions on http://code.fairphone.com but that’d be a strange reason.
I’ll tell you if it worked usind the sdcard as soon as copying finished.
If you’re using a self compiled recovery you might as well disable the zip file verification. I think this is only a hassle and does not serve any real purpose
“Applying update via sdcard” also failed for me with both OTA zips (1.1.6 and 1.1.7) though the MD5s of the files match what’s in the updater.xml. Sadly I can no longer try using the original recovery system since I don’t have the .img (No one except Fairphone has, I assume).
@lklaus: Sure I could disable that. I’m just wondering why it failes on the official updates released by Fairphone 
interesting… I uploaded it via adb sideload and it worked on the very first try…
why would a custom recovery impact the installation of a standard rom? Doesn’t make sense to me…
Does not make sense, I’m simply not sure in the recovery are all keys used…
@Moritz
Hey,
Freibadschwimmer suggested to me to ask you for help here
I made some mistakes concerning getting write access to my sdcard
Now my phone is dead and I tried to recover it but I couldn’ succeed.
Which mistake have I done?
Could you help me to restore my phone?
I am a beginner!
Though I first stored the FP2-gms36-1.1.7-ota.zip on my sdcard.
Then I booted into recovery mode (at least I think so) and chose “install update from sdcard” and pointed to the ota.zip .
The phone installed it but after the reboot I got error messages like “google services are terminated” as well as Hangouts and more about google services.
I can’t finish the setup wizard because of the failure messages (google services are
terminated) and the wizard itself gets terminated. These messages began before flashing after a mistake in editing the platform.xml because the storage and the external sdcard weren’t recognized any more.
Did I make any mistake concerning the flashing?
I guess that the storage partition has to be recovered or created new?
I want the phone to be as it was delivered. What else do I have todo?
Could anybody help me because I am a bit despaired about my newe phone and begin to get hopeless.
Do I have to send my phone back to FP?
Maybe try to flash ota.zip in fastboot, as you can add -w, which does some wiping too
Hi Iklaus,
thanks very much for your advice!
I tried to reach my phone with minimal adb and fastboot yesterday night and a few minutes ago and it’s not listed.
Would the install work though?
How should be the syntax? adb…?
If you are in fastboot mode, you have to use the command fastboot, not adb.
So:
fastboot devices
fastboot flash -w ota.zip