5. Turn off Unnecessary UI Elements 
In some cases, it could be app opening animations that are making your iPhone just feel slow. While this won’t fix any software issues or bugs, if there’s nothing wrong with your iPhone it can at least give the illusion of running a bit quicker — particularly if you’re more sensitive to sluggishness than most.
To turn off these UI animations..
- Open Settings
- Tap General
- Tap Accessibility.
- Make sure Reduce Motion is toggled On.
Navigate to #4 Using the Right Arrow