PHIIT it is the original program and definitely still intense. But PHIITTER increases that intensity by changing up the combinations, adding new movements, and having less rest. Both of these programs include Level 1 which is equipment free whereas Level 2 you will just need a pair of dumbbells at a weight that is suitable for you. For PHIITTEST, you must have dumbbells to do the program.
PHIITTEST also includes even more difficult movements and combinations and less rest than PHIITTER! It is really going to push you to your limits. Also there are no low impact modifications in PHIITTEST like there are in PHIITTER. It is only for the most intense individuals.
Each program builds off each other which is why it is important to do them in the designated order to get the best results and lower the risk of injury.