;WITH SampleData AS (
SELECT * FROM (values
('8009874321', 'cars'),
('8009874321', 'Newsales'),
('8009874321', 'Newsales'),
('8009870000', 'Newsales'),
('8009870000', 'BenaSales'),
('8009870000', 'BenaSales'),
('8009870000', 'BenaSales2'),
('8009870000', 'BenaSales2')
) sampleData ([800num], CompanyName))
SELECT [800num], CompanyName
FROM (
SELECT [800num], CompanyName,
dr = DENSE_RANK() OVER(PARTITION BY [800num] ORDER BY cnt DESC)
FROM (
SELECT [800num], CompanyName, cnt = COUNT(*)
FROM SampleData
GROUP BY [800num], CompanyName
) d
) e
WHERE dr = 1
For fast, accurate and documented assistance in answering your questions, please read this article.
Understanding and using APPLY, (I) and (II) Paul White
Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff Moden