Well, technically Phoenix Air has two specially-equipped jets, but one is always used to back up the other one, so only one is available at any given time.

The lack of air transport is given as the primary reason why countries like Canada and Australia have declined to send any healthcare workers to West Africa to help deal with this latest outbreak. Cuba has, and now China will, send a lot of help to West Africa, but I don't think either of them have any proper medical transport capability similar to Phoenix Air.

If suspected Ebola cases are transported soon after symptoms first appear, experience seems to have shown the danger of infecting others appears very low, so if a situation arises where multiple people need evacuation at once, that might come into play. Some special negative-pressure, HEPA-filtered isolation "pod" may not be necessary to safely evacuate those cases.

Of course, the further into the disease a person gets, the higher the risk goes as they become more infectious, so at some point, a pod becomes necessary.