Yeah, I have a Galaxy S6 and works fine when I've lost signal. I'm using Gaia and Earthmate as I did buy an Inreach+ for piece of mind. While Earthmate Nav isn't "great" it does what it's intended for. I know GAIA you have to download maps ahead of time as well. I'm still learning the whole Nav thing, but I'm getting there. I think I need to invest in a tablet as trying to zoom and pan on a phone, Inreach or 7" screen on my Android radio is a pain. Plus then I can dedicate BT between Inreach+ and the tablet. My phone usually goes to radio for tunes.
This is why I bought a 7-inch tablet. Recently picked up an iPad Mini 3 from the refurbished section on Apple store. 128gb model with wifi+cellular. Set it up in my rig with a Ram mount.
Been working out great, and have been really happy. Also dumped my entire music library on there, so it's also doing secondary duty as the media center in the vehicle. And makes looking up things a hell of a lot easier. Plus, since I can just leave it in the craddle hooked up to the truck all the time, I can jump out and take photos with my phone a lot easier now, than having to unplug the phone, switch apps, and hope the bluetooth connect works or nothing screws up when I get back in the truck.
It's worth the investment dude, you won't regret getting a tablet. I pretty much have stopped using any other GPS devices. Gaia GPS on a tablet is fantastic.