I'd think of it in this way.
Almost everybody's screen is inaccurate.
Most laptop screens & mobiles are over-contrasty & punchy.
No two are the same.
Everybody is used to looking at their own screen & how it represents images.
If the images are accurate in the first place, the end user sees the same discrepancy every time.
This is compounded by...
If your screen is out by some random factor, you don't know what you are sending to others.
Their screen will push your already 'uncertain' image out by that much again.
The best thing you can do it make sure it's correct when it leaves your machine.
Export web images as sRGB & embed the profile.
That covers, as best as possible, how it will arrive on another screen.
Some web browsers read the profile & adjust accordingly; some ignore it & assume sRGB anyway; others just completely make it up as they go along.
Calibrate your workflow.
Buy a hardware colorimeter.
Don't ever attempt to do it by eye.
Basically the more you spend, the better it will be. Consider £$€ 250 to be about right.
X-Rite & Datacolor are the major players.
Make sure you get it right - colour workflow is a minefield.
Don't skimp. If you buy a cheap one, you'll end up having to buy another. I've now got 3... 2 of which are useless ;)
If you are on Windows & use more than a single monitor, set your best screen to be primary & calibrate that. Windows cannot use multiple monitor profiles in a workflow. Mac can. Nix idk about.
If you are aiming for iPhone, at least get an old one so you can see generally how the imagery is pushed. They're not all the same, but there's a family resemblance in how they modify colours. They do tend to be fairly accurate as far as 'RGB' goes, just a tad punchier than 'life'. You don't often find one with a heavy colour-cast, which is a plus.
If you are working from bespoke photographs, rather than image bank, the photographer needs to supply an image of his colour passport for every lighting setup.
He ought to have one of those & ought to know how to use it.
That will enable you to set a specific camera to screen workflow, via Photoshop/Lightroom etc [far too complex to describe here.]
Then your task only becomes screen to web, camera to screen is already done.
Alternatively, he needs to be responsible for sending accurate images already in sRGB.
Camera to screen is not your problem - but it may be a problem, you need to make sure it isn't.