If you want your phone to shoot like a DSLR then treat it like a DSLR

1. Use manual settings

Lowest ISO is the way to obtain the finest quality possible surpassing even iPhone's image stacking when you shoot handheld. You can easily shoot auto in excellent lighting but once it's getting dark consider using manual settings to capture at the lowest ISO. I use ProCamera app for it and couldn't find anything more convenient to me.

2) Shoot RAW

Not the housewife's ProRaw introduced in 12 pro but the real RAW. It's accessible on every iPhone since 6s and is superior than ProRaw in terms of detail, weight, processing speed but there's a catch: it must be shot at... the lowest ISO possible! There's also the new 48 mp ProRaw which is of course more detailed in daylight than any true RAW capped to 12mp max but that ProRaw is not resolving all the 48 megapixels (in fact, 24mp at most), it is always using auto settings and it can't benefit from advanced RAW denoising because ProRaw isn't a true RAW. Not to mention ProRaw weighs up to 7 times more than RAW and you can't shoot quick series of ProRaws. They both have their own advantages but RAW has more.

3) Shoot RAW... exposure brackets!

The dynamic range of an iPhone RAW is about 10-11 EV stops. In ProRaw it's about 13-14 stops. But with a RAW exposure bracket you can reach up to 16 stops! You'll have more highlight details and cleaner shadows in extreme DR situations but there's some work to do just like using any DSLR... You'll need to import your exposure brackets to the desktop version of Lightroom or ACR and merge them into HDR. I find Camera M and ProCamera to be the best for shooting EB because they do it instantly while also using OIS or IBIS (stabilization) which is important for minimizing shifting between EB frames when handheld. Most other cameras don't do that.

4) Color calibration and white balance

The default adobe RAW profiles are unsurprisingly color inaccurate. Why is the sky cyan and not blue, why is the skin tone too orange or too yellow? No one calibrated your iPhone RAW colors at Adobe that's why. To solve this problem you can buy an X-rite color palette and use their software to create a .dcp profile for your camera on your own OR buy this profile from someone who's already done that and sells it. I know only Cobalt Image who makes these calibrated profiles for iPhones, I bought one and was satisfied enough. The second part of the equation is the white balance. To achieve the perfect neutral photo temperature you must shoot dozens of RAWs in sunny and cloudy weather conditions (or even with different types of artificial lighting if you need) in order to see what's the most common WB value. Then you create your WB presets with them for each lighting type. Be careful because a WB value from the main camera might not look the same on tele or ultra wide cameras. You must shoot dozens of RAWs using all of your back cameras! And so when your camera fails to nail the WB in let's say a cloudy greenish forest you can use the precise WB presets you created instead of eyeballing it.