1. Search for a route
You can check for existing routes in Wikiloc. This routes are designed to be checked from the official Wikiloc app, which requires paying a fee.
2. Download route
Choose the option of downloading trail. Select any of the standard formats, like GPX or KML.
3. Install free trail viewer app in your phone
There are many trail viewer applications for mobile OS.
GPX Viewer is an example of freemium application. It is available in Android and iOS.
4. Import trail to the free trail app
The free app should have an option to import trail from most common standard formats (like GPX or KML).
Once you have imported it, you will be able to check it offline on your phone.