Increase or decrease the volume during a call

During the middle of a conversation, is it possible to press any
buttons on the phone to increase or decrease the volume.

The above applies to one user who has a slight hearing impairment.
So I don’t want to do this on system wide basis.

But I would like to do this on any phone, as needed.

i would think this would be more a feature of the phone rather than asterisk…i understand what you are asking, but i highly doubt asterisk can do it (unless it’s a meetme room) and i’m not even sure it’s appropriate.

if you use headsets, there are some specifically designed for those individuals that are hard-of-hearing - perhaps one of those might work well?