Having a web app as well would have been slightly better, especially if it works in feature phones(In several developing countries feature phone usage is lot hi

Having a web app as well would have been slightly better, especially if it works in feature phones(In several developing countries feature phone usage is lot higher than smartphones even then they didn't publish a web app) but still doesn't help those who doesn't use a phone at all(whatever the reason might be). Distribute free phones which is capable of running these COVID apps and then the issue comes down to just privacy. Alternate physical form seems reasonable. *just : Not to reduce the importance of privacy(EFF commentary in my other comment).