iPhone always writes OSS when attempting to type the word is.

Greetings bobbybray,

To isolate the behavior, let's have you check and see if there's a text replacement set up for the word "is". To do so, take the following steps on your iPhone:

1. Tap Settings
2. Tap General
3. Tap Keyboards
4. Tap Text Replacement
5. Swipe left over any text replacements you wish to delete

You can see further details here: Save keystrokes with text replacements on iPhone - Apple Support

Let us know if that helps.

Kind regards.

Thanks for clarifying this for us, bobbybray,

You can set up a text replacement so that the words you type come out as you'd like them to as outlined here: How to use Auto-Correction and predictive text on your iPhone, iPad, or iPod touch - Apple Support

"Set up text replacement

With text replacement, you can use shortcuts to replace longer phrases. When you enter the shortcut in a text field, the phrase automatically replaces it. For example, you could type "GM" and "Good morning" would automatically replace it. 

To manage text replacement, tap Settings > General > Keyboard > Text Replacement. 

• To add a text replacement:

1. Tap the Add button .
2. Enter your phrase and shortcut.
3. Tap Save.

• To remove a text replacement:

1. Tap Edit.
2. Tap the Remove button, then tap Delete.
3. Tap Done."

Take care!