Matomo (Piwik) will automatically track visits on mobile phones that use browsers executing Javascript: iOs based devices such as iPhone and iPad, Android based phones or any other modern devices (running Palm Pre, Opera Mobile, Webkit, Mozilla Fennec, etc.). For low-end mobile devices that use browsers which do not execute Javascript, you can manually record visits using the Matomo Tracking API. Learn more about the Matomo Tracking API. See also Does Matomo track visitors without Javascript?

For Mobile phones using a Mobile App, you can use the iOS SDK and Android SDK to track app sessions.