Sending calls to zoom voicemail if external number doesn't answer?

Basically, it's going to boil down to ring time. If your Zoom phone voicemail max wait time is set to a long ring period and your cell phone voicemail is shorter, then the cell phone voicemail will answer before Zoom voicemail will. I ran into this issue with my Cisco Webex number doing the same and shortening my Zoom voicemail max wait time resolved it for me.

Thanks for replying. I don't think this worked. I have the max wait time set as short as possible (10 seconds). 

My apologies. I didn't catch that you setup conditional call forwarding. I don't see an option to route the call back into Zoom voicemail since you're sending the call to an external number. I've seen this option on other voicemail platforms but haven't seen it in Zoom. 

I'm not sure it will work in this cirumstance but when using call handing you want to turn on "Require to press 1 before connecting the call" this will prevent the voicemail from being left on a cell phone.