Re: IPhone SE
Your phone will work well as a GPS type device for navigating. I don't use an app but have read about some that sound good. I just cache the google earth imagery while I have service. However you will not be able to call for help if in an area of no service and the battery life is not as good as the GPS units. On an extended trip you would need a battery back like RJ mentioned. I now have the Inreach66i for rambling, mushrooming and solo hunting because I'm getting up there and it gives others peace of mind when I'm out and about. It has been used a lot by family members at a family cabin and has worked well for messaging. It depends what you want you want to do.
"Bullshit doesn't need to be countered by anything, just called out for what it is." Edward Teach