To send a voice message on an iPhone using the Messages app, follow these steps:

1. Open the Messages app and select an existing conversation or start a new one.
2. Tap the plus "+" button located next to the text input field.
3. Tap "Audio" from the menu that appears. This will start recording your voice message immediately.
4. Speak your message.
5. When finished, tap the "Stop" button.
6. You can tap "Play" to listen to your recording or tap "Send" to deliver the voice message.

Alternatively, you can also press and hold the microphone icon in the message field to record and send a quick voice message as soon as you release the button

. Note:

• Voice messages sent via iMessage may expire two minutes after being listened to unless the recipient chooses to keep them.
• Both sender and recipient need to be using iMessage on Apple devices to send and receive voice messages this way.
• For longer or permanent audio recordings, you can use the Voice Memos app to record and share voice memos via Messages or other apps

This method works on iPhones running iOS 16 and later, including the latest iOS 17