Iphone 12 macboock air Colour Grading Issue

Hi, Im new so I dont have the lingo so please try dum it down for me.

Im using rec 709 as all the solutions have said. When I edit a video and export it, the colour grading is always way off. Even when I dont touch the colours. Pics for example.

How do I use adobe premier without it messing up my colours, or do I need to find a different software? 

See attached examples