I’ve always enjoyed using the Windows Phone app on my Mac. IMHO it works better than the corresponding app on Windows. I upgraded my Mac to El Capitan this week and when I connected to the Windows Phone app over the weekend, it remained on the initial page stating “Connect your Windows Phone to continue”. Usually it starts syncing shortly after I connect. Not any more. I’m running the current version 3.1.1 (140416) and tried to connect using a Lumia 520 and an HTC 8x. Both phones are running the current phone OS (8.1). The Mac Photos and iPhotos apps do not see any photos on the phone either. I thought I’d post this so someone else may be forewarned.
Update: As of Tuesday, Oct 6, 2015, the Windows Phone app was no longer available through the App Store.
Look here for a solution (third post on that page):