If these are the same ads I see on a Google search (image below), Pi-hole doesn't block them since the ads you see are from the same domain as the content. It is only when you click on one of the ad links that you are directed to a different domain that Pi-hole can block.
For comparison, this is what I see on that site using the basic 5 blocklists:
Given that you only see ads on the iPhone, it is possible that the iPhone has another DNS server available and the DNS requests are not all going to the Pi-hole.
You can check and see how the ads are being served using these tools: