Phantom rewrites the transaction before you sign. It adds compute budget instructions and a Lighthouse safety check for each account the transaction writes. Lighthouse is Phantom's own guard. It checks that the accounts end up in the expected state and fails the transaction if not.
So an app buy can show more instructions and a larger size in the wallet than the app built. That is normal. If the wallet shows an action you did not ask for, such as an unrelated transfer, reject it.