Headphone jack works intermittently, seems like software issue?

My headphones only seem to work if I toggle on and off between speaker phone and headphones. For example, someone calls, my headphones are plugged in, I answer, nothing works, i flick it to speaker phone and then immediately back to headphones and they work again. This happens irrespective of what I'm doing. Listening to music, texting, talking on the phone. Any ideas?

(Yes tried rebooting phone, Ios up to date)

Thanks.