Looked on the phone.. looked in the manual -- it seems that this model of phones does NOT have a mute feature! (mine isn't the exact one in the picture but it is a Uniden 5.8GHz 2-handset model purchased in 2009) There only mention of Mute in the manual is muting the ringer (i.e. making the handset not ring) which is different.
So, sorry, there is no way to start cursing at your relatives or boss without them hearing you.
Answers & Comments
Looked on the phone.. looked in the manual -- it seems that this model of phones does NOT have a mute feature! (mine isn't the exact one in the picture but it is a Uniden 5.8GHz 2-handset model purchased in 2009) There only mention of Mute in the manual is muting the ringer (i.e. making the handset not ring) which is different.
So, sorry, there is no way to start cursing at your relatives or boss without them hearing you.
You can find the manual for your phone at Uniden's website, it will list the features and how to use them.
Push the mute button