How do I put in a volume control on this wired phone headphone set?
I have this headset which I use with a cordless handset.


I'm assuming you will use (or want to use) this headset exclusively with the cordless handset so it isn't a problem modifying it.

If you can get to the speaker terminals then try putting a 100 ohm resistor in series with each speaker. This should attenuate things a bit. If still too loud then try a 330 ohm resistor, Hey they're 3 pence each (at most) so experiment a bit.

If potentiometers are your ultimate aim then experimenting with the resistors will get you an approximate value for a pot ohm wise. Without the little experiment you might be needing a ten ohm pot or a 1k ohm pot.

You ought to consider soldering this modification.