The iPhone/Android PowerSchool apps are not allowing student and parents/guardians to fully set up their accounts. Right now the only way to set up your account to log in for the first time is to use a computer or Chromebook. After you have set it up and have logged into your account for the first time on the computer/Chromebook, you will be able to use your new username/password to log into the phone app.
This is a PowerSchool app issue that they have been made aware of. We have no control over this issue.