Virulence effector that plays a role in hijacking the host vesicular trafficking by recruiting the small guanosine triphosphatase (GTPase) Rab1 to the cytosolic face of the Legionella-containing vacuole (LCVs). Acts as a phosphocholine transferase by mediating the addition of phosphocholine to Ser residues of host RAB1 (RAB1A, RAB1B or RAB1C) and RAB35, leading to displacement of GDP dissociation inhibitors (GDI). Phosphocholination of target proteins also impairs accessibility to GTPase effector LepB. Can act on both GDP-bound and GTP-bound Rab proteins. [Rab1 protein]-L-serine + CDP-choline = [Rab1 protein]-O-phosphocholine-L-serine + CMP + H(+) Translocated into the host cell via the type IV secretion system (T4SS). The FIDO domain mediates the phosphocholine transferase activity.