Is four the right age to start phonics?
Four is a reasonable age to start sounds, and usually too early to push reading. Those are different things, and conflating them is the single most common reason home phonics goes badly. A four-year-old can happily learn that the letter m says mmm, can hear that "cat" and "cap" start the same way, and can clap the beats in their own name. Expecting them to read a sentence by five because a neighbour's child does is a different matter entirely, and it is where the pressure that puts children off reading comes from.
The National Education Policy 2020 places ages three to eight in a single Foundational Stage precisely because this is a long runway, not a race. Some children blend words at four. Many do not until well into Class 1, and those children are not behind. The variation at this age is enormous and says almost nothing about how well a child will read at eight.
So the answer is: start, gently, with sounds. Ten minutes a day. Stop if it stops being fun. Everything below is written for a parent with no training and no materials, including parents whose own English is not strong - if that is you, our guide on helping with English when you cannot speak it well yourself covers that specific situation in more depth.