The f phoneme sound can be be made by 5 different letter or letters. The more commonly known spelling for the sound is higher up the page with the more unusual ones lower down.
The video says the word; then breaks it down into the individual phonemes, highlighting the letters that make the sound, blending them together to show how the word is formed. The phonic alphabet symbol, representing the sound, appears in the top right hand corner.
Click the alphabet letter button on the right of the screen to learn its other phoneme sounds.