The android phone such is made by LG, Samsung and others can over time become cluttered with software and files and unusable,
this can affect the speed of operations and even call quality

This can happen naturally over time as older phones have poor quality housekeeping and do not regulate their storage very well..
Can also happen because of the millions of applications out there, a few of which you may have on your phone which have been found to cause problems by snooping and behaving badly; Google often finds out about these and disables them, but not always.

Ideally you would have access to a second completely empty android phone and simply switch over. You do need to check the Google account you used on your phone which is the account it uses to back up your contacts and other information onto the Internet in the so-called cloud.

You can visit https://contacts.google.com first, on a webpage on a separate computer ideally and be sure to use the exact same account as exists on your phone right now (some people have more than one Google account… )
to see that your important contacts and phone numbers are indeed stored in the google Cloud.
What you see there is what will come back after you have reset the phone and put the Google account back in

Other stuff will be backed up as well; Be sure you have the right password!
but possibly important things may not be backed up such as text message history