Contributes to the overall PI4-kinase activity of the cell. This contribution may be especially significant in plasma membrane, endosomal and Golgi compartments. The phosphorylation of phosphatidylinositol (PI) to PI4P is the first committed step in the generation of phosphatidylinositol 4,5-bisphosphate (PIP2), a precursor of the second messenger inositol 1,4,5-trisphosphate (InsP3)