A VPN creates an encrypted tunnel between your phone and somebody you trust, such as the company you work for, or your VPN provider. Your phone traffic is routed through the tunnel, where its protected from surveillance, before joining the internet. Using a VPN on an iPhone can bolster the overall privacy and security that users have come to expect from the Cupertino-based phone maker, which has gone to court to fight back against efforts to downgrade its mobile operating system.”]
Source: https://blog.malwarebytes.com/privacy-2/2021/03/the-one-reason-your-iphone-needs-a-vpn/