Why is the speaker icon missing on my iPhone 13 keypad?

Do you mean the speaker button when you're in an active phone call? If you receive a call you should see the speaker icon which you can tap to answer the call AFTER you swipe to answer the call. If you make a phone call, you should see a phone icon at the top of your iPhone once the call is active and if you tap the green phone icon, the options, including speaker should then appear.