DS (also winter-born) is similar. He was all over numbers before he started school in September, but letters - nope. He showed initial interest in phonics when term began, and fell in love with "Geraldine the Giraffe" at school (Google Mr Thorne does Phonics on YouTube if you haven't come across it), but half a term in it's still not really gelling and his enthusiasm is waning. He came home upset this week because they had been put into "reading groups" at school and he is in a different group from his little friends.
Like you, we have books everywhere at home. Like your son, DS is articulate and very talkative, has a great vocabulary, and will listen to stories or chapter books for as long as an adult is prepared to sit reading to him.
We are putting absolutely no pressure on him and doing our utmost to maintain the joy in books and reading. We are answering comments like "I don't know the letters" or "I'm not very good at reading" with "You don't know them YET". We are emphasising that some things take time to learn and reminding him that he's done things before that took a lot of perseverance, like learning to walk, and then to talk!
We have bought the Dandelion Launchers series of decodable books to give extra practice at something that's within his reach. He can have a crack at them and feel a sense of achievement (unlike many of the school reading books at, supposedly, the initial book band level). He does pick up a "read it yourself" book as he calls them, from the Dandelion Launchers series, every few days and there is progress, but it's slow. DS enjoys the Nessy Letters and Nessy Phonics apps which give lots of multisensory practice with the letter sounds.
We are also continuing with all the basics we were going at preschool age, like lots of "I Spy" games to tune into the sounds in words. Maybe back up a bit and play with pre-reading skills and listening for sounds?
FWIW we are aware that DS is at familial risk of dyslexia as both DH and BIL are quite profoundly dyslexic and there's supposed to be a 50/50 risk of it being passed on. It's too early to tell whether DS does have an underlying difficulty, or whether reading is something which is just going to click with him later on, or take longer than average to pick up. A dyslexia screening test is standard at the end of Yr R (separately from the Yr 1 phonics screening) in all local schools around here. Worth keeping an eye on if reading continues not to gel with your son over the next term or two?