That is the way the application is designed. You can access the basic voicemail through the dialer by dialing *86 or long pressing the 1 key. You can also create a contact called voicemail and save the voicemail access number and your password if you want.
I'm most definitely NOT a VZW employee. If a post answered your question, please mark it as the answer.
The Voicemail app can access either Basic Visual Voicemail which is free. Or the premium which cost around $2. Alternatively, you can still access the voicemail through *86 or dial your own number even if you have the Voicemail app installed.