Currently to transfer to voicemail on a physical phone requires several steps,
While on a call, press the Transfer key.
If your phone's default Transfer type is already set to Blind, proceed to the next step. Otherwise, press the Blind softkey.
Enter *0 (asterisk zero) and then the target extension number.
Wait for a couple of seconds for the transfer to complete automatically, or press the # (Hash key) to dial out.
I suggest programming a softkey with the option to transfer to voicemail with a single press instead of having to go through multiple steps