can i still back up my iphone if the screen is broke

Yes. Just do the usual procedure with itunes

Maybe. I say that because if your device is locked with a passcode, it is very possible it will prompt you to unlock the device via the passcode on the screen. You may not be able to do that with the screen damaged. Without being able to unlock the phone, you would have to use the latest backup you have.

Hello,

As The two above posts say - It's not usually a problem.

what if i have no previous backup and screen is cracked so i cant enter passcode? how can i backup

Unfortunately, you cannot. That is why regular backups are important. You will only be able to use your last backup before the device was damaged. If you have no backup at all, then your content will be lost.

my iPhone 6 is broke and i can't retrieve my history messages and calls