MS Word allows setting height to rows (tr), not to cells. You can check it opening MS Word, adding a table and then changing the properties.
phpdocx supports setting height to rows as well, you just need to add the height property to the row. The library adds this property using "atLeast" values; if you need to set "exact" values, please use the addTable method or DOCXCustomizer. You can also customize the generateTrPr method in HTML2WordML.php.
Since the release of phpdocx 9.5, the easiest approach to accomplish this task is using HTML Extended.