I know this works with phones other than iPhones. not sure about iPhones.
Dial your number from any phone. When your voicemail picks up, hit # and then follow the prompts to hear your messages.
Did you have "find my iPhone" set up on your phone so you could possibly find it? Be sure to report it as stolen to the police and to Verizon so that you do not incur any charges you shouldn't.
Good luck and Happy Birthday.