Yes, in many cases, the "f" sound in the word "of" is not pronounced when it is followed by a word beginning with a consonant sound. This is an example of a phenomenon called elision, where certain sounds are dropped or not fully pronounced in connected speech for the sake of ease and efficiency.
For example:
"Piece of cake" might be pronounced as "piece uh cake," with the "f" in "of" not fully articulated.
"Cup of coffee" might be pronounced as "cup uh coffee."
However, when the word "of" is followed by a word starting with a vowel sound, the "f" sound is usually pronounced. For instance, in "cup of tea," the "f" sound is typically pronounced.
It's important to note that pronunciation can vary among speakers and in different dialects of English.