Some of that is pronunciation, some of that is grammar.
फूल "phool" - flower (Sanskrit origin)
फूलों "phoolon" - flowers
फ़ूल "ful" - foolish (loanword from English)
The initial consonant of फूल is an aspirated /pʰ/, much closer to /p/ in English "pull" than to /f/ in English "full". (In theory.)
In practice, the respective initial consonants are undergoing a merger all across Hindi and even some inconsistent use of the distinctive dot in the written form can already be encountered. They are on their way to become homonyms.
However, the singular/plural distinction is going to stay.