MUTEAUDIO Feature not working

mute_on => 1,self/caller,Set(MUTEAUDIO(in)=on)
mute_off => 2,self/caller,Set(MUTEAUDIO(in)=off)

exten => 6003,1,SET(DYNAMIC_FEATURES=mute_on#mute_off)
exten => 6003,n,Dial(DAHDI/1/10,tTK)
exten => 6003,n,Hangup()

Then I entered asterisk -rvvvv, and issued the features reload and the dialplan reload command. The features reload command shows that it recognizes are registers the dynamic features.

I enter into a phone call with phone 6003. It is an old analog phone with no mute capability. While in the active call, I press the “1” key. The CLI indicates that the digit press is recognized and displays

Feature Found: mute_on exten: mute_on

However, its not working. I can still speak into the analog phone and my voice is still heard on the other phone.

Anyone have any ideas?