array_unique($data, SORT_REGULAR);

Array
(
    [0] => Array
        (
            [First Name] => xyz
            [Last Name] => abc
            [Primary Contact Email] => xyz@hotmail.com
            [Preferred Telephone] => 1-123-000-123
        )
    [1] => Array
        (
            [First Name] => xyz
            [Last Name] => abc
            [Primary Contact Email] => xyz@hotmail.com
            [Preferred Telephone] => 1-123-000-123
        )
    [2] => Array
        (
            [First Name] => dss
            [Last Name] => sddfs
            [Primary Contact Email] => dss@hotmail.com
            [Preferred Telephone] => 1-553-000-123
        )
    [3] => Array
        (
            [First Name] => dss
            [Last Name] => sds
            [Primary Contact Email] => dss@hotmail.com
            [Preferred Telephone] => 1-444-000-123
        )
    [4] => Array
        (
            [First Name] => dss
            [Last Name] => sds
            [Primary Contact Email] => dss@hotmail.com
            [Preferred Telephone] => 1-553-000-123
        )
)

Array
(
    [0] => Array
        (
            [First Name] => xyz
            [Last Name] => abc
            [Primary Contact Email] => xyz@hotmail.com
            [Preferred Telephone] => 1-123-000-123
        )
    [2] => Array
        (
            [First Name] => dss
            [Last Name] => sddfs
            [Primary Contact Email] => dss@hotmail.com
            [Preferred Telephone] => 1-553-000-123
        )
    [3] => Array
        (
            [First Name] => dss
            [Last Name] => sds
            [Primary Contact Email] => dss@hotmail.com
            [Preferred Telephone] => 1-444-000-123
        )
)

$emails = array_unique(array_column($data,'Primary Contact Email'));
$phones = array_unique(array_column($data,'Preferred Telephone'));
$names = array_unique(array_column($data,'First Name'));