Your question can be improved by including a snippet of what you've done/tried and perhaps the challenge with that you can get tailored help with context, in any case, here's a SQL query to achieve your desired result.

SELECT
    Id,
    Column1,
    Column2,
    JSON_QUERY(YourJSONColumn, '$.PhoneNumbers[*].PhoneNumber') AS PhoneNumbers,
    STUFF((
        SELECT ', ' + PhoneNumber
        FROM OPENJSON(YourJSONColumn, '$.PhoneNumbers')
        WITH (PhoneNumber NVARCHAR(255) '$.PhoneNumber')
        FOR XML PATH(''), TYPE
    ).value('.', 'NVARCHAR(MAX)'), 1, 2, '') AS ConcatenatedPhoneNumbers
FROM YourTable;

Remember to replace YourTable with the actual name of your table and YourJSONColumn with the name of your JSON column

Edit: Optimising the query

SELECT
    Id,
    Column1,
    Column2,
    JSON_QUERY(YourJSONColumn, '$.PhoneNumbers') AS PhoneNumbers,
    STRING_AGG(JSON_VALUE(phoneNumber.value, '$.PhoneNumber'), ', ') AS ConcatenatedPhoneNumbers
FROM YourTable
CROSS APPLY OPENJSON(YourJSONColumn, '$.PhoneNumbers') 
    WITH (PhoneNumber NVARCHAR(255) '$.PhoneNumber') AS phoneNumber
GROUP BY Id, Column1, Column2, YourJSONColumn;