after the update of ios11.1 phone is gettig slow

What iPhone model do you have?

Try a restart or force restart of your device. Read the first section of the following guide:

If your iPhone, iPad, or iPod touch won't turn on or is frozen - Apple Support

Regards

Giulio

Me too. It's an iP7 running the latest iOS 11.1.1 and everything is working fine.

if restart or force restart don't help, I'd try to restore your device to factory settings so that a fresh copy of iOS is downloaded and installed, and then set it up as new.

Make a full backup of your iPhone, then follow the steps provided in the following support guide:

Restore your iPhone, iPad, or iPod to factory settings - Apple Support

After setting it up as new, test it (without restoring from your previous backup). If it runs smoothly, then you don't have any hardware problem. So you can restore from from you previous backup.

If the issue still persists, contact your nearest Apple Store and have your device inspected.

Regards

Giulio

You're welcome