I failed a drug test and had to do my time in jail. Does the VOP constitute another felony charge on my record?

No

Popping dirty won't add a new felony if that's what you mean. But just to be clear, if this was your only slip up, and you came clean the minute you toked it, poked it, snorted it, or transported it, can still land you back on the flats and 101 ways to eat TOP RAMEN. Our Justice System is not as simple as "crime and punishment." There is no such thing as a definitive punishment for each crime. There are conditions that can determine the severity for the charge, as well as add other charges. You know, conditions like negligence, gross negligence, voluntary, recklessness... ect. I hope this helps.