Fellow ADHDer - phone notifications work for me but only after sanitizing my phone notifications in general. I got rid of EVERY non-essential alert, alarm, and reminder. I don't need to know the second someone replies to me on Reddit or the moment I get a spam email or that starbucks is offering double star day tomorrow. Once I got rid of the background noise and retrained myself that 'phone only makes sound when it's important,' I had a much easier time actually getting and responding to my calendar reminders. Also made sure I used something that gave me a persistent notification, since it was too easy to turn off an alarm and 'I'll do it in just a second' (spoiler: in just a second, I would forget the alarm had happened.) Instead I'd just leave the notification untouched until I actually physically completed the task, and then clear it.