To access the voicemails, you must be designated as a Call Queue manager. Below is a link that guides you through the process:
https://support.ringcentral.com/article-v2/Remote-Member-Management-for-Call-Queues.html?brand=RC_US&product=RingEX&language=en_US&pills-nav=mobile

I’d do this:
Admin Portal > click on the call queue > Voicemail & Notifications > Settings > Add Co-recipients > add your own user ext.

this way whatever voicemails are left on the queue will also be visible in your own app. 



Here you can also “Edit” Notifications > switch to advanced settings in the top right corner > Customize notification for voicemail > Make sure that voicemails are sent to your email address (you can enter multiple addresses there). Make sure Include attachment is checked. 

This is much better @Problem Solver! Great tip!

The customer is getting the voicemails via the app, so that is not the issue.

They are asking how to check the message from the PHONE.  (they are old school)

ohh I thought we were talking about mobile phones & the mobile app.
If the question is regarding a deskphone, then I would still do the  
Admin Portal > click on the call queue > Voicemail & Notifications > Settings > Add Co-recipients > add your own user ext.

The user who you configure as co-recipient will be getting 2 kinds of voicemails, which he/she will be able to listen on their deskphone: 

• voicemails left to his direct number
• voicemails left to the call queue 

You might wonder “how do I know if the voicemails I got was from somebody calling my direct number or from somebody calling the call queue? I believe the only way to know is  by context. It wouldn’t be an issue if you are not expecting to get voicemails on your direct number. 

(There might be better ways to do this)