Hello, Applebug216.
We understand that Voicemail icon is missing from the Phone app. We are glad you took the time to post and are happy to help.
Does your carrier offer visual voicemail? Wireless carrier support and features for iPhone in the United States and Canada
After confirming that your carrier offers visual voicemail, we recommend going through the process to Set up Visual Voicemail on your iPhone, in particular, the section 'Get help with Visual Voicemail' of that article. Though, before you do that, we recommend that you Restart your iPhone. This straightforward troubleshooting step is quick and often resolves a number of issues.
We hope this helps.
Best Regards.