The iPhone uses plenty of motion effects when the Home Screen is tilted, or when apps are opened or closed. Leaving this on can run down the battery and has led to some reports of motion sickness.
To stop this, open Settings followed by Accessibility. From here, choose Motion and turn Reduce Motion on.
When it’s turned on, you also get the option to disable Auto-Play Message Effects. Turn this off if you don’t want to see the full-screen animations that can be sent in Messages.