Biomolecular condensates play important roles in diverse biological processes. Many viruses form biomolecular condensates which have been implicated in various functions critical for productive infection of host cells. The adenovirus L1-52/55 kilodalton protein (52K) was recently shown to form viral biomolecular condensates that coordinate viral genome packaging and capsid assembly. Although critical for packaging, we do not know how viral condensates are regulated during adenovirus infection. Here we show that phosphorylation of serine residues 28 and 75 within the N-terminal intrinsically disordered region of 52K modulates viral condensates in vitro and in cells, promoting liquid-like properties over condensate hardening. Furthermore, we demonstrate that phosphorylation of 52K promotes viral genome packaging and production of infectious progeny particles. Collectively, our findings provide insights into how viral condensate properties are regulated and maintained in a state conducive to their function in viral progeny production. In addition, our findings have implications for antiviral strategies aimed at targeting the regulation of viral biomolecular condensates to limit viral multiplication.