A phase modulation apparatus and method are provided. The phase modulation apparatus includes a storage to store phase modulation setting values corresponding to various communication modes; a phase modulation setting value selector to select, when a communication mode is changed, phase modulation setting values corresponding to the changed communication mode among the phase modulation setting values stored in the storage; and a phase modulator to modulate a phase of a transmission signal using the phase modulation setting values selected by the phase modulation setting value selector. According to the phase modulation apparatus, since a frequency characteristic of a loop filter in a PLL circuit is changed depending on a transmission mode of a communication apparatus and phase modulation is performed using appropriate bandwidths according to various transmission modes, it is possible to prevent noise characteristics from degrading when a PLL bandwidth changes.