Plays critical roles in regulating RNA replication and transcription through its interactions with multiple proteins (By similarity). Tethers the RNA-directed RNA polymerase L to the nucleoprotein-RNA complex (By similarity). Recruits the M2-1 protein, a processivity factor that is required for efficient transcription of viral RNA (By similarity). Acts as a chaperone for neo-synthesized nucleoprotein by forming an N-P complex that preserves N in a monomeric and RNA-free state and prevents the association of nascent N with host cell RNAs (By similarity). Recruits the host phosphatase PP1 to inclusion bodies to regulate viral transcription (By similarity). Together with the nucleoprotein, sequesters host NF-kappa-B in inclusion bodies (IBs) thereby inhibiting this host defense pathway (PubMed:32878896). Homotetramer. Interacts with protein M2-1; the interaction between the two tetramers is required for the anti-termination and elongation transcriptional activities of protein M2-1. Interacts with host phosphatase PP1; this interaction recruits PP1 to the inclusion bodies. Formation of a complex PP1/M2-1/P allows P to target host PP1 phosphatase to the M2-1 substrate. Interacts (via C-terminus) with the nucleoprotein N (via N-terminus); the phosphorylated phosphoprotein P binds to N-RNA complex. Interacts (via N-terminus) with the monomeric RNA-free nucleoprotein N. Interacts (via C-terminus) with RNA-directed RNA polymerase L; the association of P and L forms the polymerase complex. Localizes in cytoplasmic inclusion bodies. The N-terminus is important for viral particle assembly. The oligomerization region is central. The C-terminus part contains binding regions for the RNA-directed RNA polymerase L and the nucleoprotein. Constitutively phosphorylated by host. Phosphorylation at S-116, S-117, S-119, S-232 and S-237 is required for transcription inhibition by M2-2 and viral particle egress. Phosphorylation at S-232 and S-237 increases the affinity of the binding to the nucleoprotein. Belongs to the pneumoviridae phosphoprotein P family.