Because the English language is so rich and diverse it is very difficult to create a phonics system that caters for all. Every region that speaks the English language has its own accent which means there are always variations in the way that a word is pronounced.
Across England we all spell words the same but we certainly do not say them all the same, even though we all use the same 44 sounds. In the English language the 44 sounds can be represented by over 280 letter combinations.
So, accents have arisen from regions applying different phonemes (sounds) to graphemes (letters) when they pronounce words. The regions still use the same sounds and letters, they just associate them differently.
For example, in the South of England the letter ‘a’ can be pronounced as the ‘long ’R’ controlled’ vowel sound /ar,(ɑː)/ in words such as ‘grass’ and ‘bath’ whereas in the North of England it will be pronounced as the ‘short’ vowel /a,(æ)/ sound in these two words.
Click and then scroll down the page to see the animations of the different pronunciations of the word ‘bath’. https://www.teachphonics.co.uk/teaching-phonics.html#pronunciation
Both pronunciations are correct, which can make teaching phonics a little tricky; the key is to teach the sound to letter relationships which best suit the children being taught in relation to their regional accent. It is important to remember that children’s knowledge of the sounds that make words is based on how you speak to them naturally and not a strict standardized set of sounds.
However, for general educational and learning purposes the English language’s phonics system has been standardized, this is known as the ‘Received Pronounced’ (RP) English, and is used in comprehensive English dictionaries and translation dictionaries. The RP is based on a southern accent sound to letter relationship basis.