The only solution to solve this problem is rebooting the phone, there are many steps to that, I am posting them below, please try them one by one, unless it reboot.
Top 1. Use Home Button
To unfreeze an iPhone, the first thing you should do is to press and hold down the Home button for about 6 seconds. Then you will be returned to the Home screen with everything working again.
Top 2. Restart iPhone
When your iPhone 6 frozen on Apple loading screen, what are you supposed to do? Actually, all you need to do is press and hold the Power button until a red slider appears on the screen. Drag the slider to power off your iPhone. Then press and hold the Power button again until the Apple logo appears. Wait a few seconds for iPhone's startup sequence to finish and you can be back at the Home screen.
Top 3. Reset a Frozen/Hung iPhone
If holding down the Power button cannot work to reboot when your iPhone 6s freezes after unlock, you can reset it by holding down the Power button and Home button at the same time for about 10 seconds until the Apple logo appears.
Top 4. Close an App
If you have a single misbehaving app on your iPhone, you can "force quit" it by pressing and holding Power button for a few seconds until a red slider appears, then press and hold the Home button until the app quits.
Top 5. Remove Some Content
If your iPhone screen is still frozen, you can try to remove some of the content that's on your iPhone. Alternatively, you can erase all content and settings by tapping Settings > General > Reset > Erase all Content and Settings. Then you can use the Top 2 method to restart your iPhone.
The methods below are about how to reboot a frozen/hung iPhone without Power or Home buttons. If you have a broken Power/Home button, try any of them until you can restart your iPhone and fix the issue.