The best solution I have found (Android only) is an app on Google's Play Store, called “Bike Tracker” from PC Ability, which I have now used to successfully guide me round probably about a dozen rides, of between 20 and 50 miles. Best thing ... it's FREE ! It works with both GPX and TCX files.
The app works with RideWithGPS on your PC, one of the few mapping tools that automatically produces the “cue” sheets required for turn by turn navigation. Here you can find loads of routes in your area and just take a copy of the GPX file, or edit the route to make a new GPX file, make your own route from scratch and create a GPX file, or you can import GPX files from any other source on the internet. Its worth checking that the GPX file has “cues” at each junction, telling you to “turn left” / “turn right” / “go straight ahead” / “stop for a pint at the White Lion pub” or whatever. These are the instructions you will hear while cycling the route. If any “cues” are missing, you can add new ones (or edit/delete existing ones).
To follow a route, start the Bike Tracker app on your phone. You can download the routes you have created with RideWithGPS to your phone while still at home, using your wifi, and then just load the route when you are ready to ride. The app does not use your phone signal, it just uses the GPS signal on your phone. Press the GPS button on the screen, and when ready, press the Start button. The app will give you rough directions to the start point of the route, and once at the start, the “cues” created on the route will then guide you round the route. Enjoy the ride.
To hear the turn instructions, I bought a waterproof Bluetooth loudspeaker mounted on my handlebars (mine was off Amazon for £20 which is also a headlight). My phone is stashed safely in my bag and does not provide any distraction - I don't need to constantly check a map, as the app will tell me if I have strayed off the route and gives instructions on how to get back to the route. Alternatively, you could mount your phone on your handlebars, or use earphones (the new bone conducting Bluetooth earphones are probably the best option, as you can still hear traffic noise around you).
"Bike Tracker" - works for me. Try it.