You're in luck, because Tolstoy's major works are in the public domain, which means there are a lot of free and legal options. Project Gutenberg is probably the most reliable source; they have clean digital versions of 'War and Peace', 'Anna Karenina', 'The Death of Ivan Ilyich', and others. The formatting is straightforward, just plain text, but it's accurate.
For a slightly nicer reading experience, Standard Ebooks takes those public domain texts and formats them into more modern-looking EPUBs. They're also free. I'd steer clear of random websites that promise 'free' versions but are full of ads or might have weird typos. It's worth the extra minute to get it from a reputable archive.
Honestly, reading 'War and Peace' on a phone screen can be a slog, but having it for free on an e-reader app makes the commitment a bit easier. I still prefer a physical copy for the really long ones, though.
Another route is your local library's digital service, like Libby or OverDrive. You need a library card, but then you can borrow professionally formatted e-books and audiobooks legally. It's not 'owning' a free copy, but for a single read-through, it works perfectly and supports libraries.