iPhone locked in "headset" mode

I need help unlocking the "headset" mode. I was using my earphone last night and now my iPhone is locked in that mode. I can only make calls using the speaker phone, which doesn't work well in most public settings. I can use my bluetooth just fine, but still, don't want to keep that thing attached to my ear all day.

I've tried turning the phone on and off - no luck. Went through the settings, but can't seem to find anything called "headphone settings" on the actual phone. Help!