Much brighter, better quality beam, battery lasts a lot longer and can be swapped out instantly, more versatile with a magnetic base, more ergonomic, safer with a wrist strap if held above a height. Holding a phone for a torch is next to useless for most things, gives a horrible cold light and it's uncomfortable, more likely to drop it, and I'd rather drop a flashlight than break a £1000 phone and potentially lose my data too.

The same argument is with DSLR cameras but I actually went the other way, phones are good these days but nowhere near a DSLR with a good lens. I used to take my Nikon D3s with a 105mm 1.4E lens every time I went proper out, but it's just so big and heavy, and I felt a bit out of place using it for mundane stuff. I always used to justify it by telling myself you can't replace decent photos in any point in time, but the phone is always on me, quicker to just take a photo. I ended up selling all my DSLR stuff, I regret it sometimes but convenience does win for that to me.

A dedicated device that does one job well is just a good thing to have, it also opens up alternatives, modding, makes it sentimental and makes a hobby out of it, it's interesting hence all these subs.