Yes, it's possible to log in to Schoolrunner on your phone, but we do not have an app for parents and students. Right now, the only app we have is for teachers and it's not possible for parents and students to use it.
Schoolrunner is designed for computers, but you can log in to Schoolrunner via your phone's browser if you'd like. You'll need to know your login address. It will look something like YOURSCHOOL.schoolrunner.org. You'll just have to replace "YOURSCHOOL" with the correct name (domain) for your school.
You may have gotten a document with your username and password that looks like this, and which lists your login address:
If you have any questions, ask your teacher for the correct address.