looked in to this myself a while ago most IR camera's work by picking up IR which your plants will give off a small amount of even in there night cycle, fancier camera's have a bulb/LED's giving off light in the IR spectrum, those are what you want to avoid as they might possibly trigger the hormone change that plants go through from dark to light, though they need to put off a fair amount of energy to do so, these sorts of camera's are mostly used in security systems and are prolly out of your price range anyways
the issue is the streaming to your iPhone, if it's on your home network someone outside your home can crack your network, use a scanning tool, find IP's internally with weird ports open and boom they see you've a camera on a grow, how plants you have, and at what stage they're in
if you want it so that you can check on them from outside the building the grow is in then you've 100's of security issues to consider to stop the above happening
or you can try get a camera with a bluetooth connection to check from out side the tent but this again has security issues
or build an arduino setup and have a hard wire coming out and physically connecting to a monitor (screen, tablet, smartphone)
TBH it's just easier to accept that when it's dark they're just the same as when the light is on, only you can't see them.