Thank you for the answer. On the phone headset, the difference is that the connections for earphone and microphone are in a combined plug. I don't know how they are arranged; I could imagine that inserting the wrong plug might short-circuit some lines that shouldn't. OTOH the plugs might be designed in a way that this will not happen.

celtschk‭ A "headset", as the term is often used, is nothing more and nothing less than an earpiece and a microphone somehow combined into one unit. If it lacks a microphone, it's simply a set of headphones. What kind of plug it has (if any; consider wireless units) is unrelated to that designation.

Canina‭ That is why I explicitly specified phone headset. That's the one with the combined plug. While computer headsets have separate plugs for microphone and earphone, thus for those indeed there's no difference to separate devices, as far as this question is concerned.

Mobile phones have used 2.5mm and 3.5mm headphone sockets and also headset sockets. The headsets usually make provision for barrel, tip and TWO ring contact. The connection arrangement differs between the old Apple phones and the typical Nokia/Android types and many laptops also support a headset system to save on a connector and support standard phone headsets.

In most cases a device that is intended to drive a 64Ohm headphone or headset and a possible microphone parasite power will survive any combination of incorrect plugging in but will not work when plugged in wrong.