First try restarting the device. It may just be a glitch that it isn't listed. If that should not resolve it you can try downloading a file manager app from Google Play. However, I am not sure the original phone app will be there.
If you really wanted the original app(s) on the phone, the only way I know for certain that you could get it would be a "Hard Reset". However that would wipe the device, so you would have to back up all your person files elsewhere (google, cloud account, computer, etc.) and you would have to reinstall all personal apps after the reset. Should you wish to do that, the instructions on how are below.
NOTE: Doing this will clear 'all' the data on your phone, so it is suggested you not choose this option unless...