Hi there! I understand you're having trouble finding the Gusto app in the Apple App Store on your iPhone running iOS 18.5.0. Let's work through this together.

First, can I ask:
- Are you searching using the exact name "Gusto" or "Gusto Mobile"?
- What region or country is your Apple ID set to? Sometimes apps may not appear if they're not available in your region.
- Have you checked if any restrictions or Screen Time settings might be limiting app visibility?

Meanwhile, here are some steps you can try:

1. Search directly via the Gusto app link: You can try to open this link on your iPhone's Safari browser, which should take you directly to the app page in the App Store: Gusto Mobile on the App Store

2. Check your App Store region:
- Open the Settings app.
- Tap on your Apple ID at the top.
- Tap 'Media & Purchases' > 'View Account'.
- Tap 'Country/Region' and confirm it's set to the US or a region where Gusto is available.

3. Disable Screen Time restrictions:
- Go to Settings > Screen Time.
- Scroll down and tap 'Turn Off Screen Time'.
Just to rule out if any app restrictions are hiding the Gusto app.

4. Restart your iPhone: Sometimes a quick restart can refresh the App Store's search functionality.

If after these you still don't see the Gusto app, it could be a region or account-specific issue. Let me know how these steps go or if you've already tried any of them!