Can consider Sony rx100 if you have the budget. No need to get the latest version lah. Maybe one or two years ago gen good enough for your use. It's portable, good lens, can record at 4k and easy to use.

Where are you going though that makes you extra concerned over low light scenes?
Anyways the rx100 would give you better quality than any phone camera by virtue of the sensor size itself.
In the end have to consider that the best camera is what you have at hand and how you handle it.
Iphones generally shoot pretty good video. Even your iPhone 7 can produce good vid, maybe just get a mobile gimbal for steady footage.