There is a variant of this phrase: "get a hold of". "Get hold of" and "Get a hold of" are mostly interchangeable, but "get hold of" is more often used when talking about people (e.g., "get hold of Mr. Jones and tell him...") while "get a hold of" is used with things (e.g., "I think I've finally gotten a hold of this concept...").
Thanks a lot. Your explanation was really useful.