Went on a scuba diving boat today and noticed when I got back my iphone6 stuck in headphones mode as I was filming people jumping off boat and splashing into water. Thought salt water must have gone in the jack hole and dried leaving salt crystals.
TRied all the techniques listed here, cotton bud tip that was soaked in methylated spirits in attempt to disolve/ dislodge any salt or grime.
Still would not work, then while playing around with volume buttons and sending some txts I got two text messages back from some friends and this fixed the problem.
The sound from the message being received somehow reset this iphone earphone stuck 'bug'
Very happy Chappy as I don't need to go to a service shop to pay for repairs.
In summary, after cleaning earphone jack with cotton bud dipped in ethanol or methylated spirits allowing to evaporate and dry, get someone to text you a few times making sure you have a sound enabled for incoming texts.
IPhone 6 back to normal