If your voicemail is standard just tap and hold the inbox to get the dropdown for the other folders.
When you see the symbol next to the red arrow in the pic above that is indicating there is a dropdown menu available.
Have included links to the support pages for your phone below.
Have a good one.
Boost support site:
»
www.boostmobile.com/supp ··· y-sii-4gUser Manual:
»
www.boostmobile.com/shop ··· _sii.pdf