What is the make and model of your phone please? And did you mean your phone screen is frozen?
How long have you been facing this issue? Apart from the crack, is the on button functioning fine?
It could be because of a hardware damage. Anyway, let's try some basic troubleshooting.
Hold down the power button and the home button together for 10-15 sec. Let me know if you get any apple logo.
If it does show an apple logo, check whether your issue is resolved.
Even after rebooting if the slide to unlock does not work, I am afraid it is more of a hardware damage and may need a repair or replacement.
However, we can also try a complete restore of the phone to factory settings and see if that would resolve the issue. I believe you may have a backup of the iphone either in icloud or in itunes in the computer (so that after a phone restore, we can recover the data).
Open itunes in the computer and connect the iphone to the computer. If your iphone is recognized by itunes, click on the iphone logo listed in itunes and now, to the middle of the screen you will find a button called "backup iphone". Click on that to backup your phone. After backup is complete, click on the button "restore iphone"and restore it. Let's see if that works.
okay. let me know if you find any difficulty.