Blocking Ads in Safari on iPhone 5
There is no way to block ads using Web Restrictions, so far as I know.

You do have two options for blocking ads, though, which I will explain below.

Note: if you do have an iPhone 5S or newer, you should stop reading and just use Content Blockers, which are by far the most desirable option. However, if you do still sport an iPhone with a 32-bit chip (iPhone 5 or earlier), here are two ways to block ads:

Using a VPN

You can use an app like Opera's new free VPN to block ads and trackers in any app, including Safari. Basically, once you set up their VPN (which is actually free and has no restrictions), all of your internet traffic will be routed through one of their servers, where they remove ad-related content and send the rest to your phone. 

Advantages of Opera's VPN: 


Ads are blocked in all apps, including Safari.
No cost
Also anonymizes your IP address and secures you on insecure Wifi networks.


Disadvantages of Opera's VPN:


Internet speeds may be slowed considerably (in my experience from 75mbps to 9mbps at its slowest)
Opera can spy on everything your doing, but they're a fairly trustworthy company and probably aren't doing that.


Using a different browser

Your other choice for blocking ads in web browsing is downloading a separate browser app that has ad-blocking built-in. This is the one I would choose, simply because of all the disadvantages of using a VPN. I have used Brave Browser a lot: it's a simple browser that replaces Safari but works just as well (it remembers passwords for you, blocks ads, increases security with HTTPS Everywhere, and works with password managers like 1Password). It's entirely open-source, and made by the engineer who co-founded Mozilla.

Advantages of Brave Browser:


Ads are blocked
No cost
Uses HTTPS Everywhere to increase your security
Can't spy on all your other internet traffic
Works great as a day-to-day browser
Doesn't slow your internet speed like a VPN does


Disadvantages of Brave Browser:


Doesn't block ads in your other apps
Doesn't make Safari ad-free





I hope this guide has helped you, if you have any questions please leave a comment below and I'll comment back.