You can still block ads on a DNS level. Simply add, base.dns.mullvad.net as your primary DNS Server and that should do you a lot of good just there. I'm sure there are additional steps one could take as an iPhone user though.
Don't have an IPhone so wouldn't know, but that does seem annoying indeed. It is possible to just change your DNS on the router instead. And or use a VPN that also includes a different DNS.
It is, though. Safari has native support for 3rd party adblockers, it’s just that many people don’t know. AdGuard is one of the good options. Safari is doing the actual blocking for the most part (the extension just hands over the filterlists), but nowadays some of the adblockers include an optional extension that applies some rules for complex ads that are not supported by the Apple API, such as on YouTube. As an end user you just have to install and enable the adblocker.
Then there are also other browsers available with built-in adblockers. Admittedly those are all limited in some ways because they’re forced to use the same browser engine (outside of the EU), but they are very effective at blocking ads.
I've used this for several months and just switched to Mullvad DNS. It blocked ads on pretty much everything. Between that, using a VPN, and uBlock on Firefox, my mobile browsing experience is pretty nice.