This would be a pretty lame conclusion without really checking out what’s going on with the phone.
There are demanding Apps out there, yes, but the Fairphone 2 is still perfectly fit to run most of the Apps normal users use every day.
If storage turns out not to be the issue …
https://support.fairphone.com/hc/en-us/articles/210512123
https://support.fairphone.com/hc/en-us/articles/115001610926
In the Android world, a factory reset contrary to its name doesn’t set the phone back to the state in which it left the factory. It doesn’t touch the installed OS at all, it just deletes user data and Apps, and the phone starts with the initial setup again.
In most cases, that’s a sufficient reset of the phone, but if not …