Productivity might improve slightly, but there isn't enough time within any particular phase to make up time. More generally, do not assume that a schedule slip at any point in the project can be made up later. If the project doesn't catch up soon after a slip is detected, you can safely assume that it won't be possible to catch up. Don't relax standards in order to cuts costs or shorten a schedule. Relaxing standards tends to introduce errors into the project, and optimum project cost and schedule both depend on eliminating errors.
Relaxing standards can also have a demotivational effect.
Most developers are quality oriented, and a relaxation of standards sends the message that the customer or upper management doesn't care about quality. Don't assume that a large amount of documentation ensures success. Different projects require different kinds of documentation support. Determine the amount and kind of documentation required based on the project size, schedule, and expected lifetime of the system. This book is a software survival guide.