Apple and Google are trying to get more U.S. states to adopt their phone-based approach for tracing and curbing the spread of the coronavirus by building more of the necessary technology directly into phone software. That could make it much easier for people to get the tool on their phone even if their local public health agency hasn’t built its own compatible app. The tech giants on Tuesday launched the second phase of their “exposure notification” system, designed to automatically alert people if they might have been exposed to the coronavirus.