Generally speaking this is true. However, in some cases, phase 3...

Generally speaking this is true. However, in some cases, phase 3 studies can be skipped, or accelerated approval may be given.

A situation in which a phase 3 study may be skipped entirely is when a drug has been demonstrated to be bioequivalent to an approved drug (eg what happened with Rexista XR).

Accelerated approval may be granted when there is significant unmet need for a drug. This allows a company to start selling the drug while using data generated from sales to conduct a study of efficacy. As an example:

"The FDA granted “accelerated approval,” meaning Lilly could sell Lartruvo but would get full approval only if a follow-up study confirmed a clinical benefit. Patricia Keegan, a division director at FDA, says she and colleagues knew the early study had confounding factors, “but we didn’t know how to weight them” against the apparent benefit, she said. “We were aware it was imperfect.”

While we would never qualify for the first example, if we demonstrated a significant improvement over current treatments for various cancers then an accelerated approval is a possibility. Not at all likely, however still possible.