I have this (NZTopo50) as a back-up, but it has nothing on the NZTopoMaps app for map resolution and functionality - in my humble opinion. Disclaimer that it may have improved since I looked at it, but the NZTopo50 maps pixelate when you get to any useful (for me) level of zoom. I asked the developer if they could have downloadable/cached areas with better quality, and I think this was something they were working on, but unfortunately, not in a timeframe that suited me.
Back to the OP's original query, a good compromise between dedicated GPS and your day to day phone that you don't want to drop in a creek could be these phones:
https://store.blackview.hk/ Mega battery size, IP68, and generally pretty functional. I bought one for an overland motorbike trip. Does everything you need it to, and more. Battery lasts forever. Uses 4 different GPS systems, and I think the new one even has a thermal camera built in... seems like a gimmick, but you never know.
I could dig mine (bought in 2019) out for you if you want to give it a go before buying? Hasn't been charged up for a year or two, but should still work. New ones should also have an e-sim option.
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