I want to use my old iPhone as a cam in my coop

I don't think I'll be able to get it on the wifi accept when I go out to the coop with my current phone and can use my hotspot. I can keep it plugged in and charged all the time though. Does anyone else do this? I'm curious as to which App you've used and had the most success with.
I tired to look if this was already in a thread but didn't find anything in the couple searched I did.
Thanks in advance for your help!