How can I stop my iPhone from auto-correcting 'I'?

Accidentally you may have used this feature.

You can utilize the Text Replacement feature on your iPhone to save time and enhance productivity by storing commonly used phrases, sentences, or even emoji combinations. With this feature, you can assign custom shortcuts (keywords) to phrases, making it quick and easy to insert them into messages, emails, or any text field.

For example, you could set up a shortcut like "omw" to automatically expand into "On my way!" or use "addr" to insert your full address. Similarly, professionals can use this feature to quickly type standard replies, email signatures, or frequently used jargon.

To set up Text Replacement:

1. Open the Settings app.
2. Navigate to General > Keyboard > Text Replacement.
3. Tap the + button in the top-right corner.
4. Enter the full phrase in the Phrase field and the shortcut (keyword) in the Shortcut field.
5. Tap Save.

Once set up, typing the shortcut will trigger the full phrase to appear as a suggestion. Tapping the suggestion or pressing space will replace the shortcut with the full phrase. This feature works across apps, saving you time and effort while typing.