Even though I am glued to my phone most of the day, and I use it to set alarms for simple stuff (like: take your pills!), i actually use paper and pen, and lots of different colours so that different tasks or different places to go stand out.
Ticktick! There’s a quick add widget which has made it super easy to put new things up right when they come to your mind. Only that kind of app that has worked even somehow for me. Maybe a bit more to do type app but!
Pomodoro app (basically twenty minutes of doing work, followed by shorter breaks, followed by doing more work for 20 minutes) is super helpful!
In terms of routine and adding big structure to your day, I’ve started using the Fabulous app, which is part well-being builder and part routine-builder. You have the option to create routines in each major part of your day (morning, afternoon, and evening) and which habits you add to those routines are entirely up to you. I’ve been doing my Morning Routine (which helps me get ready for work in a timely manner) for about two weeks now, and adding habits to it as I go. It’s really helped! Bonus - you can add time estimates to habits, and the Fabulous app automatically totals up the time, so you know in advance how much time the entire routine will take to complete. The premium membership is 100% worth the $46.
The only thing I wish the Fabulous app did that it presently does not is have the ability for you to add individual, one-off tasks throughout your day and remind you of them. Then it could really have a go at replacing my bullet journal, since the app is also beautifully designed and comes with a slate of its own sounds and ringtones.