In this phrase, "别太放肆" means "don't be too unrestrained" or "don't be too unruly." "没什么用" means "it's useless."
When translated into English, the phrase means something along the lines of "Don't be too unrestrained, it's useless." This could be interpreted as an advice to refrain from being overly wild or reckless, as it may not lead to any productive outcome.
In terms of pronunciation, there is no direct English equivalent for this phrase. However, it can be loosely translated and pronounced as "Don't tie fang si, mei shen me yong" in English.