Any process that results in a change in state or activity of a cell or organism (in terms of movement, secretion, enzyme production, gene expression, etc.) as the result of a phenylpropanoid stimulus. The process begins with detection of the stimulus and ends with a change in state or activity or the cell or organism. A phenylpropanoid is any of secondary metabolites with structures based on a phenylpropane skeleton. The class includes phenylpropanoid esters, flavonoids, anthocyanins, coumarins and many small phenolic molecules. Phenylpropanoids are also precursors of lignin.