Hi William:
That's exactly how it's supposed to work, by design. The assumption is, when you are calling from a mobile phone number, you want to listen to your voicemail messages, so it does not ring the other forwarding destinations.
If you want to change this behavior, then go to the old "Legacy" version of Google Voice settings. Click the Edit button under the cell phone number. On the next page, change the phone type to either "work" or "home" (it makes no difference) and save the setting. After doing that, when you call your GV number from your cell phone number, it will ring the other destinations first. If you do want to hear your voicemail messages, press * to barge into your greeting, and then you'll be able to access the voicemail menu.