OSM = Open Street Maps. They're routable, have POIs, etc. But they're free. You can buy detailed maps, but the OSM ones are free.

I use my GPS cycling computer for navigation. It's way more convenient than using my phone, for many reasons. Easy to see in bright sunlight, waterproof, 20 hour battery life, the maps are on the device, it talks to my HRM and power meter. Remember, a lot of the riding I do is in places where my phone doesn't get a signal. Sometimes it's spur of the moment. I'm not willing to spend the time pre-loading maps onto my phone before every ride, especially when my GPS already has them.