Sounds like you plan to use WiFi from phone to streaming PC (OBS). Correct?
Hopefully you realize all that can go wrong with trying to use WiFi that way, especially if that PC then uses WiFi to connect to Internet to stream. It might work, and easily might not. Will ANYONE else be using WiFi at the same time?
Other than the latest WiFi standards, usually WiFi acts like a walkie-talkie.. [1 device talking at a time, wait for response], so beware
A wired connection from iPhone is an option
If no option but WiFi from iPhone, then for reliability, make sure PC is using wired connection to router/Internet, and that all other WiFi devices are turned off (simply not sharing WiFi pwd doesn't disable beaconing and other discovery activity, so though not likely, depending on number of devices, and especially if they were allowed to use WiFi before, could create a problem
Being respectful of others health, if indoors there should only be celebrant and person running PC. In which case, as Facebook is limited to 720p, a webcam may work much better (what I'm doing at the moment). We don't expect a hybrid service (in-person/sanctuary) and remote viewers for quite some time (next year at earliest.. maybe, could easily be year after if vaccine rates aren't high)
Regardless of webcam or smartphone/tablet, all use wide-angle lenses which means having the camera up close to celebrant. Which will be distracting if you have other attendees. To support a hybrid service, I recommend a camera with a telephoto lens (a DSLR with nice lens can work, or a PTZ camera (what we are ordering... significant lead time on them at the moment)
Also, beware of the difference of going live on FB, vs a Scheduled Live event (both set up from
https://www.facebook.com/Live/Producer/ ). The benefit of a Facebook scheduled event is that non-Facebook users can watch from pretty much any browser and see comments [URL listed when you create event... as well as the requirements which include connecting ahead of time.]
As we plan to use a NDI PTZ camera, our plan is to use the NDI app on an iPhone. Recent YouTube reviews have indicated a free Android NDI app may work as well as the NDI version.... but I don't know for sure either way. I did play with obs.ninja, which is a free service, and it worked fine for me.