Negatively regulates cilia formation by recruiting the CP110-CEP97 complex (a negative regulator of ciliogenesis) at the distal end of the mother centriole in ciliary cells (PubMed:30375385). At the beginning of cilia formation, MPHOSPH9 undergoes TTBK2-mediated phosphorylation and degradation via the ubiquitin-proteasome system and removes itself and the CP110-CEP97 complex from the distal end of the mother centriole, which subsequently promotes cilia formation (PubMed:30375385). Interacts with CCP110, CEP97 and KIF24. Localizes to the distal and proximal end of centriole pairs in duplicated centrosomes. In ciliated cells, localizes to the distal and proximal end of daughter centriole and proximal of the mother centriole but not in the distal end of the mother centriole (PubMed:21399614). Recruited by KIF24 to the distal end of mother centriole where it forms a ring-like structure (PubMed:30375385). TTBK2-mediated phosphorylation at Ser-629 and Ser-636, promotes its ubiquitination at Lys-632 leading to proteasomal degradation, loss of MPHOSPH9 facilitates the removal of the CP110-CEP97 complex from the mother centrioles, promoting the initiation of ciliogenesis (PubMed:30375385). Phosphorylated in M (mitotic) phase (PubMed:8885239). Ubiquitinated at Lys-632, leading to proteasomal degradation. Extended N-terminus.