Appears to be a bug in 2018.1.4 (and I believe in 2018.1.3 as well) that doesn't allow the use of the Bold/Italicize buttons within the Table Tool. The two buttons remain grayed out regardless of what font you choose.
Searching the community I found a few months old post that mentioned this same issue and saying it was solved for 11.8 but I'm not sure if that was ever the case. Nevertheless, it absolutely doesn't work in 2018.1.4
