my phone is iphone 6 and the ios 11.0.1 is slow and some times stop doing anything for few seconds

I am not sure if this is the answer, but my iPhone 6s was acting like that for almost 2days after updating. I found that it had taken that long(almost 2days) to completely rewrite the iOS11 programs to APFS in the background. Having said that, if you have had this problem for more than 3 days, I suggest you check your phones activity to see what it has been up to. i.e. background activity, running programs, resource hogs. One area to check would be location services being constantly being checked by many programs. Only FIND MY PHONE, WEATHER, MEDICAL program(s), and SYSTEM SERVICES should be the ones checked as always. All others should be checked as ONLY WHILE USING. The other thing to check is an individual program constantly running as it is 32bit. If you do not need the program, now would be a good time to delete it.

Mine runs like a scalded dog.