Apple released the iOS 11.2.2 update last week to mitigate the risks associated with the Spectre chip flaw. Apple has addressed the issue in iOS 11.2.2 update patch to make iOS device’s system more secure.

However, it seems that the patch doesn’t fix the issue completely, and Apple won’t release the next iOS update quickly. Although the programmers are actively working hard to reduce the likelihood that user’s iPhone will be exploited with the Spectre flaws. Apple has made it clear that these are not outright fixes.
Apple has also warned that the iPhone’s performance will be affected. Although they shouldn’t be severe, they are noticeable in some cases. Melvin Mughal, a security researcher, has created a bit of a stir after posting the benchmarks of his iPhone 6, which shows a hit as high as 40%.
Benchmarks (iOS 11.2.1)

• Single-core: 1461
• Multi-core: 2491
• Floating Point: 1244

Benchmarks (iOS 11.2.2)

• Single-core: 1433
• Multi-core: 2440
• Floating Point: 1223

It’s a 2.5-percent performance hit, and is not enough to be noticeable with the common tasks. But if you find your iPhone is sluggish after updating iOS 11.2.2, here are the things you should do:
Restart your iPhone
It’s the simplest way to fix your iPhone. To do so, hold down the power button until you see a prompt, slide the button to the right, and wait for your iPhone to turn off completely. Then boot it up again.
Check your storage
Low storage is the main culprit for your iPhone slowdowns, so you should check the available space by going to Settings > General > iPhone Storage. From there, there will be a breakdown of how much storage is being used on your iPhone as well as which apps are using the most. You can then delete or offload it.
Reset safari cache
If the sluggishness comes from Safari, you should reset the browser cache. Launch Settings app, and scroll down to the Safari and tap on the Clear History and Website Data section. Tapping on it will delete all your history, cookies, and browsing data. If you want to keep your history, choose Advanced at the bottom, and tap on Website Data > Remove All Website Data at the page bottom.
Disable JavaScript
As the iOS 11.2.2 version directly affects JavaScript, it could properly be the culprit in slowdowns that you feel in Safari. Go to Settings> Safari tab> Advanced and you’ll see a Javascript switch turned on by default. Turn it off and you can disable JavaScript for Safari browser, which will help some pages load faster. Since disabling it could cause issues with some of the sites, so if you have the serious issues, return to the settings and switch it back on.
Also read: How to remove Music Player widget from Lock Screen
Replace a new battery
Apple has admitted slowing down the performance of some older phones to compensate for declining battery life, so it might be the main issue. You should take your iPhone to Apple Care center to swap out your aging battery and replace it with a new one to bring your performance back normally.