Was this the official Electroneum app you were using? It sounds very much like your phone was actually being used to mine some coins. The last I heard, the iOS Mobile Miner hadn't been launched yet and was only available for Android devices currently. What's the name of the app you've been using?
I don't have an iPhone, so I can't check whether Electroneum has been approved for iOS yet. Maybe another user will be able to shed some light on this.