I wouldn't fully agree. Yeah, modern flagship phones shoot insanely well, but an action camera is a completely different thing. I was on a hike just last week, brought my iPhone and Insta360 X4, and here's what I figured out: the phone is better for photos and content videos where details matter. But for dynamic scenes, when you're jumping over rocks or riding a bike, the action camera beats it by like twice as much. The stabilization is way better, the wide angle is actually super useful, and most importantly - it won't die after a day of active shooting like your phone will.
Plus there are moments when it's just dangerous to use your phone: during a tough climb, near waterfalls when there's spray everywhere. You can strap an action camera to your backpack, helmet, or mount it on a stick - and it just works on its own while you're free to move around. Honestly, I saved up for a month for the Insta360, and I don't regret it. If you actually want to properly document your route and come back with some sick videos, better get an action camera. GoPro is the expensive option, but there are more budget-friendly good alternatives.
Just keep in mind though: footage from an action camera sometimes looks "too extreme" if you're not planning to film actual action. For calm mountain panoramas, your phone will give you a more natural-looking result. Maybe the option with both cameras - a tiny camera in your backpack, your phone for keepsake photos?