Phonics can help in spelling but spelling is a harder process compared to reading. Spelling requires many similar concepts as reading, including sound (phonological) and written language (orthographic). In spelling, the child must be able to use his phonological awareness skill to break up the words into their sounds and then recall which letter or letters match the sounds. And because the same sounds can be spelled in different ways, the sound to spelling matching is not always straightforward.
I had a child who was able to spell ‘we’ after some practice but when I introduced the vowel team ‘ee’, she spelt ‘we’ as ‘wee’. I praised her for her effort and explained the meaning of “wee” and then asked her which one made sense in the context of the sentence. ‘We’ is also an open syllable and the vowel ‘e’ is a long e.