Don't know how to forward unconditionally to voicemail

I’ve read this forum and google alot but perhaps not enough…
As regular freepbx extension , I need time to time to forward unconditionally all calls directed to me, to my voicemail instead.
This operation , for ease of use, should be done with a single key (programmable) in a sip phone or by mean of web user portal.
I’ve understood basically I have to forward calls to *myextension to activate immediately my own voicemail
I found two ways (both not practical):
from phone:
*72 myextension # * myextension # (you have to wait vocal prompt, you can’t assign such of a string to a key)
from user portal:
forward to a non-existent extension and reducing no answer time (affects usual no answer forward)

In user portal -> Phone Features -> Call Forwarding-Unconditional is not possible to set *myextension as target

As this should be a per-user feature and not a system feature, is there any other quick and practical way to forward all calls routed to an extension IMMEDIATELY to its voicemail ??

Thank you