Best malware protection for iPhone?

Well, one can find anything and everything on the web.

iOS is very secure.

Unauthorized modification of iOS can cause security vulnerabilities, instability, shortened battery life, and other issues - Apple Support

Whenever a security vulnerability is discovered, Apple quickly issues a software update. Always keep your iPhone updated.

Due to the system architecture of iOS/iPadOS, unless jailbroken, your iPhone is not susceptible to traditional malware infection per-se. However, as with all computer systems, there are still vulnerabilities and exploits to which you remain vulnerable. For older devices, no longer benefiting from regular security updates, the risk of an unpatched vulnerability being exploited increases.

Be wary of an often repeated myth that Apple devices are immune to malware; those that perpetuate this fallacy, perhaps with good intention, do not necessarily comprehend the broader threat landscape. Apple expend considerable resources in developing and issuing regular software security updates and patches for its products; if the myth had any substance, this would not be necessary.

The majority of threats to which you will be invariably exposed will surface via web pages or embedded links within email. These browser-based attacks can largely be mitigated by installing a good Content and Ad-blocking product. One of the very best and most respected within the Apple App Store - designed for iPad, iPhone and Mac - is 1Blocker for Safari.

https://apps.apple.com/gb/app/1blocker-for-safari/id1365531024

1Blocker is highly configurable - and crucially does not rely upon an external proxy-service of dubious provenance. All processing takes place on your device - and contrary to expectations, Safari will run faster and more efficiently. 

Unwanted content is not simply filtered after download (a technique used by basic/inferior products), but instead undesirable embedded content blocked from download. A further benefit on metered services, such as cellular connections where you data may be capped or chargeable, this not only improves speed but also saves you money. 1Blocker has also recently introduced its new “Firewall” functions - that are explicitly designed to block “trackers”. Being implemented at the network-layer, this additional protection works across all Apps. Recent updates to 1Blocker has introduced additional network extensions, extending protection to other Apps.

A further (strongly recommended) measure to improve protection is to use a security focussed DNS Service in preference to automatic DNS settings. This can either be set on a per-device basis in Settings, or can be set-up on your home Router - and in so doing extends the benefit of this specific protection to other devices on your local network. I recommend using one of the following DNS services - for which IPv4 and IPv6 server addresses are listed:

Quad9 (recommended)

9.9.9.9

149.112.112.112

2620:fe::fe

2620:fe::9

OpenDNS

208.67.222.222

208.67.220.220

2620:0:ccc::2

2620:0:ccd::2

Cloudflare+APNIC

1.1.1.1

1.0.0.1

2606:4700:4700::1111

2606:4700:4700::1001

Use of the above DNS services will help to shield you from “known bad” websites and URLs - and when used alongside 1Blocker, or other Content Blocker provides defense in depth.

There are advanced techniques to further “harden” iOS/iPadOS (such as using DoH, DoT and DNSSEC). Apple has recently introduced its new Private Relay to its iCloud+ subscribers - in part employing ODoH as an element of this new functionality.

I hope this information and insight proves to be helpful. 

Your own common sense.

Where did you read that? A non-jailbroken phone cannot be hacked, get a virus, or get malware.

I’m guessing you read this on a site that was selling such a “malware protection“ product, or they were advertising such a product?