Apple released an iOS patch (11.2.2) last week.
This patch reduces the risk associated with the Spectre chip vulnerability. It will make your iOS device more secure but will not completely eradicate the issue (this can probably never be completely dealt with via a software fix as the vulnerability is within the chip itself)
Apple has said there maybe a small impact on the performance of the iPhone by installing the 11.2.2 update but tests have shown it may be as little as 2.5 %, in my view, a hit worth taking for increased security.
Macworld has an article about the performance hit which can be viewed here.
I would advise installing this update as soon as possible, better to be safe than sorry.