Well, at least primarily rely on a map. I do tend to carry a compass in less familiar/more challenging situations but for hiking on trails a map by itself will generally do the job.
Some people are talking about situations that would be very challenging without GPS--low visibility/no trails--and I'd just say that I'd definitely want backup in those conditions. I wouldn't want to depend on a single phone.
I definitely agree with this. If you're in a situation where a map is failing, you probably have bigger problems than what the GPS would help with. It is also a situation where I don't think anyone but advanced hikers/backpackers should be in. Edge cases shouldn't set the standards.
Some people are talking about situations that would be very challenging without GPS--low visibility/no trails--and I'd just say that I'd definitely want backup in those conditions. I wouldn't want to depend on a single phone.