why my phone is hanging so much?
because of many years of usage.
Which OS are you on? If you're on iOS 8.x.x, it's going to have lag issues. But there are things you can do. To help your 4s run as smooth as possible, try these suggestions.
1. Leave 20% or more of your internal storage space free. This helps to not constrain the system.
2. Get rid of unnecessary features. Yeah, some are cool, but they will bog down an older model phone.
3. Disable transparency effects. Toggle on "Increase Transparency" in Accessibility.
4. Toggle off "Background App Refresh".
Good luck.
This was obviously for a 4s. I don't know what phone you use. You didn't say. It makes a difference, so when you ask for advise, let us know which phone you use. Thanks!
Sent from my ancient but trustworthy iPhone 5