Read the fare rules. You will not be able to answer your question without reading the detailed fare rules text.

Generally speaking, domestic fares represented as flexible are fully refundable.

However, given that airlines are allowed to deceptively market fares as flexible that are not actually flexible (i.e. those nefarious refundable less fee international fares), you need to read the detailed fare rules text to be sure.

It's disgusting that the DOT doesn't regulate airlines properly and prohibit them from advertising flexible fares that are not.