Make sure you use Tor Browser on your PC, and don't use Tor on your phone. To achieve higher anonymity, use Linux. Both Tails OS and Whonix are good for anonymity and privacy. If you want higher security, you can use Qubes OS as the host OS and run Whonix inside. Tails is a live OS designed to leave no traces, Whonix has a high degree of anonymity, and Qubes focuses on VM compartmentalisation to create isolation and achieve high security.

As for phones, both stock Android and iOS are bad because they are closed source and proprietary, but if you must pick one, iOS is the lesser of the two evils. You should generally go for anything that is open source, like GrapheneOS, an Android fork that is really secure and hardened. PureOS is also really good for privacy but AFAIK it only works on Purism devices. LineageOS is also a valid option although it is less secure than typical Android.

What phone OS you should get may depend on the type of phone you have, and if you have a specific OS in mind then you need to make sure your phone is compatible.