messages icon has disappeared from my i phone

I understand that you cannot find your Messages app on your iPhone. What I cannot find anywhere in your post is which iPhone you are using and which iOS version is running on it. I will have to make a guess at a resolution for you.

If you are using iOS version 14/15, then check the App Library to look for the Messages app. The App Library is the last Home Screen on your iPhone and you can continue to SWIPE LEFT on the home screen until you reach it. Locate the Messages app in the App Library and then TOUCH and DRAG the app out of the App Library and on to your favorite location of the Home Screen.

Axel F.

Apps can be removed from the home screen without being deleted. Go to the App Library (swipe left past your last home screen). From there you can touch and hold an app and slide it left back to the home screen.

If it was deleted, see the following from Delete built-in Apple apps from the Home screen on your iOS 14 or iPadOS device or Apple Watch - Apple Support

Restore a built-in app that you deleted

1. On your iOS or iPadOS device, go to the App Store.
2. Search for the app. Make sure that you use the exact name of the app. Find the correct name of built-in apps.
3. Tap  to restore the app.
4. Wait for the app to restore, then open it from your Home screen.