Primordial black holes (PBHs) can catalyze first-order phase transitions (FOPTs) in their vicinity, potentially modifying the gravitational wave (GW) signals generated during these transitions. In this talk, I will introduce the catalytic effect of PBHs and discuss how it can consequently modify the phase transition GWs spectrum. Generally, PBHs induce two key effects. Firstly, they promote the formation of larger bubbles by enabling nucleation earlier than background, which tends to amplify the resultant gravitational waves. Secondly, PBHs accelerate the phase transition process, an effect which can lead to suppression of the GW signal. At the end of the talk, I will discuss the implications of PBHs from phase transition interpretations of the PTA (Pulsar Timing Array) signals.