iPhone plays/pauses/skips songs and activates siri only when connected to earphones
You need a new headset.

The symptoms you are describing is because the "controller" assembly of your headset (the part that has the buttons and the microphone) is failing; most likely due to moisture (or some other contaminant) getting in and interfering with the circuitry.



I have had this happen to me on several occasions and not just limited to Apple headsets.    Get a good quality headset that is also water resistant like the Bose SoundSport and you shouldn't have this problem again.  (Going on 4 years with my Bose where I wouldn't last a year with the regular ones).