Did you know that you are carrying a 3D magnetometer? That you can use your phone as a pendulum to measure earth's local gravitational acceleration? That you can turn your phone into a sonar?
Phyphox has been checked for viruses and it has been found totally secure. RWTH Aachen University is the official developer of the tool which can be found in the Educational category. Google Play shows that this application is rated 4.4 by its users.
The app was downloaded and installed by over 0,5M users and the latest stable release was on Oct 10, 2020. Get the free .apk file of phyphox 1.0.6 and have a look at users' reviews on Droid Informer. This installation package occupies 3 MB of disk space and it can be launched on Android devices 4.0 and above.
Users write reviews pointing out that the strong side of the app is a good UI.