I need help

Why can’t I update my phone and always getting a phone storage full alert

Probably because you don't have enough space. You're not going to win the argument with your phone if it consistently tells you it has insufficient space.

The other option is to update the iPhone through a computer. See Update your iPhone, iPad or iPod touch with the Finder

If you're using a Mac with macOS Mojave or earlier or a Windows PC see Update your iPhone, iPad or iPod touch with iTunes

See if anything here helps. 

Disk space - How to check the storage on your iPhone, iPad, and iPod touch.    *

 Disk Space – Free Up    -

 Disk Space – Free Up (2).  -

 Disk Space – Free Up (3).  -

 Disk Space - Free Up (4)    -    

 Disk Space - Free Up (5)   -  

ASC YouTube for how to free up space on your iPhone, iPad, or iPod touch