How to detect Virus on iPhone?

iOS / iPadOS devices cannot be hacked or infected with Viruses / Malware / Spyware *** unless you have intentionally downloaded spurious software or unauthorized apps directly from the internet and installed them on your device or/and have Jailbroken. 

Be judicious when sharing the device's sensitive and valuable information with friends and family members.

**The primary reason for this is Sandboxing. All third-party apps are “sandboxed”, so they are restricted from accessing files stored by other apps or making device changes. Sandboxing is designed to prevent apps from gathering or modifying information stored by other apps.

Security of runtime process in iOS and iPadOS - Apple Support

The sandbox on an iPhone is a security feature that creates a restricted environment for each app to run in isolation from other apps and the operating system. It is a core component of iOS's security architecture and is crucial in making iPhones more secure.