I was in the same situation but I found out that restarting your phone helps reduce the amount of storage taken up by the system data. To restart your phone you need to go to settings and when you get to setting scroll and press general. Then scroll again and you will see an option that says ‘shut down’ in blue. Click that and your phone will restart. This doesn’t get rid of any of the data on your phone just the stuff that isn’t needed. Your phone will go black (how it looks when it is turned off) then hold on the power button until you see the apple logo on your screen. Now wait for your phone to fully turn on and check if it helped