iphone 6 stuck in headphone mode
was watching a video and iPhone switched to headphone mode and stuck in it
Try a forced restart of your iP6 (sometimes it helps in these circumstances):
Press and hold both the Home and the Power (side) buttons for at least 10 seconds, untill you see the Apple Logo. When it appears, release both buttons, wait for your iphone to restart, then test it.
If you get no help, try inserting (and pulling out) your headphone jack into the headphone port on your device 3-4 times, and see if this can help you.
If the issue still persists, (as suggested on the support guide that led you here), have your iP6 inspected at your most convenient Apple Store or Authorized Service Provider: Apple - Find Locations - Location Selector
Regards
Giulio