iOS Mail search function does not work properly

Thanks for visiting the Apple Support Communities, Texas iBook,

It sounds like the Search feature is not working within the iOS Mail app on your iPhone. You are already on the latest version of iOS, so we would recommend taking the following steps next. They will help us further isolate the issue, and work toward a resolution. If you've already done a step, you're welcome to move onto the next without repeating it.

1. Close the Mail app: Close an app on your iPhone or iPod touch - Apple Support and restart your iPhone: Restart your iPhone - Apple Support
2. See if the issue occurs on another network. If you're using Wi-Fi, switch to another Wi-Fi network or cellular data. If you're on cellular data, switch to Wi-Fi.
3. Check to see if the Search feature works as expected in other scenarios (such as from the Home screen, and other apps).

If you still need help after that, you'll want to get in touch with Apple Support directly. You can do that here: Get Support

Have a lovely day.