Ni-63 is a pure low energy beta emitter - what that means is your skin is enough to block it penetrating if it were outside the phone. While used as intended it

Ni-63 is a pure low energy beta emitter - what that means is your skin is enough to block it penetrating if it were outside the phone. While used as intended it would be safe but it’s a horrible idea for consumer electronics for disposal issues. Overall it sounds like a terrible idea though due to what happens when the phone reaches end of life or is smashed. Phone can’t be shredded and materials reclaimed without manually removing the battery. Phone releases free radioactive material into the environment if smashed. Terrible terrible idea for consumer electronic.