Why is the microphone icon missing from text messaging?

When viewing a message, you can either tap the App Store icon to the left of the text box and then tap the short wavelength icon to send an audio message. Alternatively, tap into the text field directing and then in the bottom right corner should be the microphone icon.

When I tap the App Store icon, there is no "wavelength icon". I never see a microphone icon inside the Messages app no matter what I do. The microphone on the keyboard just does dictation.