If not, get a transparent pillbox with compartments for every day of the week (you can also get them with separate compartments for morning / evening).
Then put it in a place that he will always see it (eg. kitchen table).
No need for an app, and it's easy to check if he already took his meds or not.
Apps or other things are kinda bad, because you can silence the alarm and then forget to take the meds, or he can accidentally take the meds twice.
If all the doses for the week are prepared ahead of time, these mistakes are not so easy to make.
Another option would be to call him every time he needs to take his pills and talk him through it. If that works, where the reminder apps don't, you could gradually switch to having someone else, like a caregiver, call him.
Another possibility is he doesn't like taking the pills because of how they make him feel but he's afraid to tell anyone.
He can check off each day on the paper calendar after he takes his pills.
If his calendar gets out of sync with his pill box, it's easy to re-sync. There's no single database.
I assume that while he probably looks at his phone every day, he definitely looks at his fridge many times a day.
If you want to get really high tech, you could add a $20 Wyze came and hang it near his pill box so you can check up on him.
I would say use this in combination with a well labeled pill box would be a good solution.
When you set the calendar entry, set both the reminder and click the repeat to choose 'daily'
https://www.amazon.com/gp/product/B004BRXI2U/ref=ppx_yo_dt_b...
It's pill box combined with an alarm clock.