When an app goes missing in your iPhone the best you can do is to use the Spotlight search feature. With this feature you can search everything on your iPhone or iPad like apps, email, search the web, iTunes and the App Store.
Start by activating Spotlight. For this swipe the screen down from the center of the Home screen. This opens the Spotlight.
Now, type the missing app’s name in the search field.
The name of the app would be seen in the top results.
In case you have hidden the app accidentally in a folder, you can find the name of the folder on the right of the search results.
In case you do not find any folder name then the app is found on one of your home screens. Find the folder by swiping through them.
Use Siri to find the app for you easily by asking it to open the app.
In case the app appears under the App Store, then that means the app is not on your device anymore.
Open the App Store app and tap on Updates > then tap Purchased > now tap on Not on This iPhone tab > find the LinkedIn app and tap on the download icon (for redownloading the app).