If you have to create and remember new workflows when on the iPhone, you won’t be able to work as efficiently; this is why universal apps are so important. Aim to use the same apps across all your devices, and you’ll set yourself up for success.
Using different apps across different devices may be alright in some cases, but most of the time I’ve found that I work best when my mind doesn’t have to shift between different apps with different interfaces. With a universal app, the transition from working on iPad to working on iPhone is seamless. There’s no wondering, “Where can I access my files? How do I change this setting?” I only have to remember one interface, with one basic layout, and one set of menus and controls. Trying to use different apps will inevitably lead to frustration over forgetting how to do something in one app, leading you to abandon the device you’re on and go back to the device and app you’re most familiar with. There are exceptions to this rule, but in general universal apps are best.