Exercise, board games, write, read a book you already own, socialise with housemates/neighbours, do any of a billion hobbies, do anything where you only have to walk to the place. Go for a walk, go foraging, sit in the sun, do some gardening, plant some seeds from your own fruit, volunteer somewhere local, draw stuff, craft stuff, daydream, do some puzzles, do some DIY repairs.

I’m not saying these things are ideal, some will be more possible than others due to circumstances. But I mean it did take two minutes to come up with that list of (typically) enjoyable stuff to do in your leisure time that has net neutral or even net positive environment impact. I don’t think it’s good to say the phone usage is the second best possible thing you can do for environmental impact.