Thanks, @feelingjuicy: Are you assuming the first and last name determine an individual? (So there can only be one Liam George.) And if not, what information would be enough to identify an individual?
(I'm also reposting your sample data so it's easy to copy, paste and use.)
sample_data <- structure(list(Email = c("jsmith@aol.com", "jsmith@aol.com",
"terry@gmail.com", "karrie@hotmail.com ", NA, "liamg2@aol.com"
), `First Name` = c("John", "John", "Terry", "Kate", "Liam",
"Liam"), `Last Name` = c("Smith", "Smith", "Jones", "Arrie",
"George", "George"), Phone = c(NA, "(222)-455-6678", "(555)-999-9799",
"(555)-456-7899", NA, "(555)-567-4578"), Address = c("665 W lane",
NA, "222 Lane St", "1234 75th Ave", "3456 Cherry Way", "3456"
)), row.names = c(NA, -6L), class = c("tbl_df", "tbl", "data.frame"
))