Collecting user
data before 2015 was actually something the company encouraged, under the banner of increased utility for Facebook users — so that
calendars could bring in information about the birthdays of friends, for instance.
Therefore, if you think that you have important
data saved on your phone (like contacts, call logs, text messages, internet settings, images, videos, audio files, IMEI / NVRAM,
calendar info, etc.),
before doing anything else consider in placing everything in safe hands — just use dedicated apps from Google Play, a computer, a SD card or a cloud storage software.