Using the phone will show you the old river runs or creek runs on the lake bottom....thats about it....You need a fish finder to see the shad and other bait fish that the crappie are feeding on and also to see the crappie and be able to tell how deep they are so you will know how deep to run your baits. You dont have to have a real expensive fish finder although they are nice....you can get by with a cheap 2 D sonar.