I use a Casio. Not just calculator, but for any tool, I try to avoid using my phone. A phone is a rabbit hole. Once you pick it up, you never know what notification will interrupt your flow. Besides, for these utility apps are difficult to monetize, it's hard to find one that isn't bombarded with ads. Even if luckily you find a perfect one, the creator might lose interest and stop maintaining it next year, forcing you to change your usage habits.