Requst for Phone update and backup

See this link about how to update your iPhone --> Update your iPhone, iPad, or iPod touch - Apple Support

Since you have likely skipped a number of updates, you will find the best success updating your phone using your home computer with the latest version of iTunes.

If you can't backup your phone, you may be out of space in iCloud. What error message do you get when you try to backup? See this link about backing up your iPhone --> How to back up your iPhone, iPad, and iPod touch - Apple Support