Hello,
The HTML you are transforming contains two br tags, so two line breaks are added in the document. Each br tag is transformed to a w:br tag (https://www.phpdocx.com/htmlapi-documentation/html-standard/insert-break-Word-document-with-HTML).
Please note that although some browsers may hide extra contents or elements based on their own specifications, phpdocx transforms all supported tags and styles to MS Word. In this case, both br tags are transformed. If you only want to add one line break, please add only one br tag.
Regards.