It is open source in the sense that you can read the source of the project, but can't really build it and use it for yourselves or verify the build you get via the App Store is the same as open source project. Practically open source as a marketing strategy.
Secondly, it needs a phone number all the time to use, which ties in with personal identity. Why? A better alternative would be a project that allows someone to choose a username and be done with it! Like HN!
The true danger of security is the false sense of it. It makes you feel okay to share personal and sensitive information. ️
I'd love for the Mattix project and riot.im to take off. Hopefully the government of France can throw its weight behind it for good causes.