Find hidden apps on an iPhone Ahappyreview?

I interpret the question as regarding apps which you know you installed but the icon does not appear anywhere on Springboard.
This happens if you have downloaded more apps than the iPhone can display.

First way:

1. Open the “App Store” app.
2. Tap “Updates”
3. Tap “Purchased”

Ensure “All” is selected on the left. Apps that are installed on this device will appear with the “OPEN” button next to them.

Second way:

1. On the home screen (Springboard) swipe down.
2. The Spotlight search field appears.
3. In the field, type the name of an app you are searching for.

Apps appear in the Applications section of the search results even if you can’t see their icons, as long as the Appliciations section is allowed to appear in Spotlight search results.