Productivity is like the most attractive girl in school. You know that you'd be great together if only you could get started. But that's scary and outside the comfort zone so why not just carry on in an angry unproductive mess?
Productivity is important because your time is important. And this is not an epic lesson on how to turn your life around. It's just pointing you in the right direction. Baby steps.
And so I'm going to suggest doing one simple thing. Organise your phone's home screen. (No really.) And there's plenty of ways of doing this (alphabetically, chronologically, thematically), you'll all find what suits you best. For me, as a visual person, I found that colour helped. It made a huge difference to my ability to remember what apps I had installed and where they should stay. Often if I'm using my phone, I'm giving it less than my full attention and so the less thinking searching I have to do, the better.