What would be the IPA symbol for 'ph', and is it different from 'f'?

I'm doing an assignment on perseveration and word errors, and I've come across an example where the 'ph' sound in one word perseveres into the next word, which is 'fool'. Are these two sounds different (ph and f)? And how would I write the sound? Do I use IPA? And would I write it in a format like /f/ or /ph/, or is there a different symbol used for that sound? Thanks so much, this means a lot to me :)