Here's a possible attempt, though it's quite forced:
"For, faintly, five foxes frolic."
This sentence uses the words "for," "faintly," "five," "foxes," and "frolic," all starting with "f." However, it's not very natural sounding and might be considered a bit silly.
It's important to note that creating a meaningful sentence using only one starting letter is often a fun linguistic challenge but rarely results in a sentence that flows naturally.