I'm a Reception teacher. I think most people have covered it already, but I didn't want to read and run.
The reason it's best to hold off formally teaching children phonics, before they start school, is simply so as not to confuse them. Some parents won't use pure sounds (suh, muh, ruh etc, instead of sss, mmm and rrr). Also, you don't want your child to become bored if they end up repeating the learning they already know in Reception.
It's much better to work on phonemic awareness before they start school, which will help them hit the ground running with reading and writing. Phonemic awareness is all about being aware of different sounds and listening out for the different sounds in words. So being able to identify the first sound, followed eventually by the other sounds which make up the word.
Oral blending comes first, before children learn to read. You can prepare your child for learning to read by sounding out instructions to him (eg go and find your h-a-t, put it in the b-i-n, sit on the m-a-t). He'll soon tune in and understand what you mean, with lots of visuals and repetition to support. Play lots of oral blending games too. You can play a cvc version of I-Spy (you sound out the object and see if he can point to it, eg I-spy with my little eye a d-o-g, a t-a-p, a b-e-d etc). Another game we play a lot is Simon says, sounding out body parts (stamp your f-oo-t, touch your b-a-ck, point to your ch-i-n, shake your h-ea-d etc). Or have fun making animal noises (eg what noise does a p-i-g make? What about a c-a-t?). What's in the bag? (Have a selection of random CVC items from around the house and sound them out for him to identify, eg in the bag is a c-u-p).
Children who have phonemic awareness usually take to reading (and writing) like a duck to water once they start school, as they've already had plenty of practice blending and segmenting sounds in words before they're even introduced to the written representation of each sound.
If you want to get more clued up on pure sounds, and how to teach blending, there are lots of videos on YouTube. Most phonics schemes are broadly similar, they might just vary the order they introduce the sounds. It's a huge money making ploy to be honest. Years back, we all taught the free government scheme 'Letters and Sounds'. Then people discovered it was a huge money spinner to invent their own scheme, costing schools thousands of pounds in training and resources which are all broadly similar. I wouldn't get too hung up on schemes to be honest. Wait until your child has their place confirmed, then you can read up on the scheme they use. They're all pretty generic though.