If you're using an iPhone with the latest iOS version, you can enable automatic capitalization which will also help in making your phone automatically lowercase. Here are the steps you can follow:
1. Open the "Settings" app on your iPhone.
2. Scroll down to "General" and tap on it.
3. Select "Keyboard" and then turn on the "Auto-Capitalization" feature.
4. Now, when you type a word in uppercase, it will automatically switch it to lowercase after typing the next letter.
Alternatively, you can also use a third-party keyboard app that supports automatic lowercase typing. These keyboard apps usually have customizable settings that allow you to toggle between automatic and manual capitalization. Some popular keyboard apps that offer this feature include Gboard and SwiftKey.