The object of your iPhone will absolutely not impede you in any way from using its antenna to transmit a multicast IP packet on a WiFi network.
It is up to you to figure out how to get the electrons in the antenna to wiggle in the appropriate manner to make that happen, but there are absolutely no constraints preventing you, as the owner of said iPhone, from doing so.
You want Apple to give you some software that lets you do that without restriction. They don’t want to. So if you want to do so without restriction you’ll have to make your own software - as in, literally replace the entire software stack, rom/os/drivers with software that does what you want.
Good luck with that, but don’t blame the device - the object you bought and own - for your failure to be able to.
It is up to you to figure out how to get the electrons in the antenna to wiggle in the appropriate manner to make that happen, but there are absolutely no constraints preventing you, as the owner of said iPhone, from doing so.