Some children will pick up spelling just through reading and some won’t. Those who don’t do need some sort of targeted teaching. Hence the recent focus on phonics. If your child is one of those who has picked it up easily, you do need to be a bit more open-minded about the fact that “they just need to read more” is not the answer for all children.
The philosophy behind phonics is that it’s near impossible to remember the spellings of every individual word in the English language, so children need to be able to recognise patterns. For example, if you can spell ‘and’, then you can spell ‘band’, ‘stand’, ‘strand’ etc, if you can recognise the ‘b’ sound/letter correlation, and the sound of the consonant blends ‘st’ and ‘str’. This way, you build up a way to spell (and read) a wider variety of words by recognising the individual components.
This recognition of patterns comes naturally to some children, some need to be explicitly taught, and some (e.g. those with dyslexia and hearing impairments), may never really be able to hear the different sounds or make the connection between the sounds and the letters used to represent them.
Research is ongoing, so yes, schools don’t know the best way to teach spelling. Methods go in and out of fashion. Education Ministers and parents with even less knowledge than schools have their say.
My advice is do everything, try everything, and if they get to the GCSE years and still can’t spell, get all the exam access arrangements you can, and in the uni years and adulthood, use the excellent assistive technology widely available.