"...within the FiOS TV app (most recent iOS, iPhone 6s Plus), I went to the Settings menu (gear icon, upper left), then Devices. I had two devices registered under my account, one from years ago and the iPhone more recently but still months ago. I Removed both devices, then re-added the iPhone. That seemed to fix the problem!!"
Wow! That actually makes logicial sense as a fix! A great alternative thing to try if/when this "out-of-home-network" error pops up since your device isn't recognizing your network. No one ever suggested I try that... Thanks!