I really do not enjoy using my iPhone for anything more than calling and texting. Maybe this is because I grew up with desktops before the iPhone was a thing - playing Snake on my Nokia - beyond that everything we did was on the desktop as that was our only real option.
As I grow older, which I feel older than I am some days, I noticed that I become frustrated using my iPhone for "tasks." Not that I can't do it, but rather the screen space just isn’t enough nor are the customization/multitasking options. It's all too busy.
I often find myself making a short to-do in Things3 to type up something later on my laptop/desktop rather than creating it on my phone at that moment.
I am sure I am not the only one out there like this, but I know it's a short list.