The hardest part is not getting an anonymous phone, but staying off the grid afterwards. Some golden rules: https://themarkup.org/levelup/2023/10/25/without-a-trace-how-to-take-your-phone-off-the-grid
For those whom security of the device is paramount, GrapheneOS is currently best-in-class. https://grapheneos.org/
@themarkup OmG attempting to be anonymous requires so many hoops, be easier to use a pay phone if you can find one?