@naltmank
I'm not a phone photography expert but you definitely can do a lot less worrying and still get really good exposures on a smart phone. Let me research some YouTubers who might be able to help you with night photography on iPhone.
I know for a fact there are more tools regarding the exposure and focus points that I don't even know how to use myself. But make sure you download the apps "darkroom" for suuuuuper easy iPhone editing and "whiteagram" makes simple white squares that keep aspect ratio of your original photo if you ever post it on instagram (which requires 1:1 aspect ratio).
Skip "beginner" Crop Sensor DSLRs
In regard to upgrading to a big boy camera, my only major recommendation would be to pass on the crop sensor cameras by Nikon or Canon (i.e. Nikon DX series - D7500, etc). I bought one when I was in university (D7100) and I outgrew them quickly. Essentially, they are almost the exact same as the professional cameras Nikon and Canon sell, but they use different lenses and have less bells and whistles. The lack of bells and whistles taught me a lot. For example, the live view didn't show you if your photo was exposed properly so I had to learn how to use my light meter and expose without seeing the live preview of what the final photo will look like.
But seriously, screw those cameras. For a bit more money you can get the real deal and it's just sooooooooo much better. If you are gonna go for a big boy camera with those brands, just go straight to full frame (i.e. Nikon FX series - D750, D780, D5).
Mirrorless vs DSLR
The whole industry is going mirrorless these days but I chose to stick with DSLR because A) I have the cockamamie "dream" of being a photojournalist and DSLR's are faster cameras but mirrorless will catch up soon, B) there are more (and cheaper) DSLR lenses available in the market currently, and C) I like the optical viewfinder more than digital-only mirrorless.
However, the whole industry is going mirrorless and you can't go wrong with a Sony mirrorless or Canon. Nikon is playing catch up with those companies but their mirrorless cameras are still good. The nerds of the camera world are like the PC Master Race nerds of the video game world so take their opinions with a grain of salt basically ever camera on the market these days is incredible.
Other options
Another good one that is small and simple but offers full control is the Ricoh GR III. It's around $1000, is the size of an iPhone, has like 24 megapixels so it's beyond print quality, and you have full exposure control with a 28mm lens that goes to f2.8. I kinda want one myself because my DSLR is massive and this thing is so damn compact and cute. It'll feel familiar upgrading from the iPhone, but not so foreign because you don't have to worry about lenses and all that.
Leicia Q is another small camera with a built in 28mm lens that goes down to a nice shallow f1.8 DOF so you can get a lot of control and fidelity in such a nice small camera.
These two cameras would be really cool step ups without going full prosumer level with the Canon's, Nikon's, and Sony's. Either way, you'll take more photos if you had one of these lil guys on hand.
EDIT:
He doesn't go into smartphone technique, but I love Sean Tucker's YouTube channel. He takes A LOT of his photos on iPhone and you wouldn't know because of how dramatic and striking they all look.
Youtube Video
