Difference between stem cell "expansion", "repopulation", and "self-renewal"?
After an hour of reading the paper (from 2014), if you can I recommend instead reading the below review article (from 2020). the 2014 article uses difficult to understand language.

Eric M. Pietras; Inflammation: a key regulator of hematopoietic stem cell fate in health and disease. Blood 2017; 130 (15): 1693–1698. doi: https://doi.org/10.1182/blood-2017-06-780882

https://ashpublications.org/blood/article/130/15/1693/36384/Inflammation-a-key-regulator-of-hematopoietic-stem

I found this by pasting your article's title into google scholar, hitting "cited by", sorting by date, and browsing until I found a review article.

The point of treating with G-CSF is that the stems cells divide, and can be recovered from the blood for stem cell treatments.

"expansion" . Here means an increase in the numbers of cells. But in plant biology it has the literal meaning of cells growing larger.

"phenotypic HSCs". Using the adjective phenotypic, the cells express the phenotype of HSCs. So the cells behave like HSCs

By itself, G-CSF makes the the HSCs divide for a while, then they stop dividing. That is, they become "quiescent".

This state of quiesence can then be interrupted. If the mice are treated with antibiotics to kill intestinal flora (or if mice are used that are germ-free), then the HSCs continue to divide.
The article calls this process of getting the HSCs to divide again "mitigating the G-CSF-mediated HSC repopulating defect"