To represent the phrase "The square of the product of 6 and a number" as an algebraic expression, where "a number" is represented by \( x \), we first identify the product of 6 and \( x \), which is \( 6x \).
Next, we need to take the square of that product. Therefore, the expression can be written as:
\[ (6x)^2 \]
So, the final algebraic expression is \( (6x)^2 \).