My Garmin fails to get a satellite lock on a train (faraday cage effect?), my phone manages it but eats more power I should think. But the garmin is waterproof, just sits on the handlebars and lasts for ages. Unlike my phone.
If the OP is any way swayed towards GPS, there are cheap options out there (£50ish +mount) for a second hand Garmin, like mine. You don't really need the maps; just upload the route via a website and perhaps take some sort of backup. There might be a couple of technical hurdles to overcome but nothing that can't be easily rectified with the right advice.
I find the reassurance and the time its saves well worth it. Plus you can get all kinds of nerdy stats.