It depends on what you want to do. To analyze charts or see things like finding rates, open interests and trade data, etc, then using a computer is better. But it comes to trade management (creating orders, closing orders, setting TPs and SLs, etc) then you need to be with your phone especially if you're going to be away from your computer, you'd need your phone to be able to manage those trades incase if goes against you and you have to close, adjust targets / stop losses.
Charting on a Mobile device is not the best experience that's why some very experienced traders even use multiple monitors.
Yes, for analysis, a smartphone is not the tool that will be your best assistant, but it can help out in some moments where using a laptop is impossible. Once I had to trade from a smartphone for several days in a row, because I was on the road most of the time and could not use anything else, and at the end of my trip I began to think that I was gradually starting to get used to it, that is, it is also possible, but it is much more difficult and requires more time for simple things that are done much easier and faster on a PC.
The only reason why using a laptop or a monitor is best suited for charting is because the larger screen offers more chart clarity, more details available to the eye. Whereas, on a mobile device, everything is jacked up so much which isn't the clearest charting screen. And yes, you're right, it's much more intuitive and fast to do it on a laptop too. Like I said, where a mobile phone shines is when it comes to trade management. You can do it anywhere, on a mobile device as long as you have cellular network.
It just depends....