If you're day trading full time and you have all the time in the world for it...and you can only choose one of those devices, which would you choose...and most importantly, why that one instead of the others?
Day trading isn't about having all the time in the world to keep looking at the trading windows and that is why mobile phone is the best this time around. You don't need to seat at home in front of monitor or desktops because you are trading, even laptops are fading away and mobile phones have rightly taken over , you can do everything with mobile phones while trading. You just need a more tech phone and you enjoy your trade from anywhere.
Just as the saying "crypto never sleeps" which is the common slogan of cryptocurrency day trading and if you're used to how they operate or know someone thats do it, you'll know that they spent almost all their time checking the chart and that's the reason why a crypto traders correction centre was established in the UK.
Not me, but I know a few "experienced" day traders — just desktops and laptops with multiple monitors. Though they use their phones to check out the charts when they're out and about(when we're out to dinner or a night of drinking), 99.9% of the trades occur on their Windows/Mac devices.
The type of trading that you spend more time on desktops, laptops or monitors can make trading very boring. That was the beginning of trading when very fast smart phones were still not out, expensive and far from the reach of newbie traders and traders who were still struggling. But you can see in your post too that with mobile phone, you can check chart, analyse trade , interchange trading pairs and do everything done with desktops including making orders.
To my understanding, the use of mobile phones happened when the trader was out as said by mk4 but they use a bot to execute 75% of their trading when on mobile or does some few update.