Another solution that worked for me - in case someone stumbles into here looking for answers. I am reposting from SteveinWA on a similar question/answer in this forum since I did not find his response until after 3 hours of searching, trial and error:
Log into Gmail, not Google Voice, on a laptop or desktop computer, not a mobile device. On your main Gmail inbox page, look on the left side of the page for your avatar. This is either a generic head and shoulders icon, or your photo or GIF that you uploaded to represent yourself. If you don't see your avatar at all, scroll all the way down to the bottom of the Gmail page, and click the small grey "chat balloon" to toggle it on or off.
Click your avatar to open up Hangouts options. Look down at the bottom of the white options box for the small link "Revert to old Chat" and click it. See my attached screenshot.
After you have reverted to old chat, click the telephone handset icon to pop up the Chat dialer to make a call. This should re-install the Chat forwarding destination to Google Voice.
After you confirm that it did so, you can reverse the procedure in Gmail by clicking "Try the new Hangouts". Your Chat "phone" will not go away.