Disclosure before we start: I build the native iPerf3 apps for iPhone, iPad, Mac, and Android mentioned near the end. Everything in this post also works with the free iperf3 CLI on two computers. The phone enters the picture when one endpoint has to move around the building.
Source: [Dev.to](https://dev.to/chamav/measuring-real-lan-speed-from-a-phone-with-iperf3-3644)