If he's talking lots that's a good thing. Are there particular letters he struggles with?
Theres actually a lot of sounds that aren’t age appropriate until 5 or 6 years old. If you want to practice start with the individual sounds, can he hear and copy them correctly? I teach nursery and a lot of the S+L reports come back as mostly age appropriate as long as the understanding is there
https://speechandlanguage.org.uk/help-for-families/talk-to-a-speech-and-language-advisor/ You can also book a free chat with a Speech and Language therapist via Speech and Language UK :). They are super helpful and will be able to tell you if there are things to do to support. Xx
My son is the same. We are seeing Speech and Languge next week so I will see then what they say. We did see a speech and language privately a while ago and she said he is behind but should catch up and may need some sessions when he is further along to help pronunciation but not to worry x