The sound “fr” suggests fragmentation. Freckles are fragments of melanin. French fries are fractions of potato. Human fractures make one frail.
A frog jumps to and fro, especially when frightened. Froth results from friction in fluid.
A frizzy hairstyle—i.e., an afro, sometimes called a “’fro”—resembles freed or frothy hair.
The phoneme “fr” is also about smell and its absence, with “fruit,” “fragrance,” and “frangipani” giving off scent, while “frost,” “frozen,” and “freezer,” are devoid of odor.