"vital phase" is a correct and usable phrase in written English.
It can be used to refer to an important period of time in a process, such as "The startup phase of our project was a vital phase that would determine the success of the entire endeavor."
For Israel, the business of recruiting informers is a vital phase of the fight against terrorism.
We are heading into a vital phase of the project that will determine whether Amref's work really makes a lasting impact.
He will be invaluable as the government embarks on the next, vital phase of its mission to restore our economy to growth and reform our public services".
As an incurable optimist, I'm hoping this will be the year we look back on as a vital phase of America's recovery from its post September 11 insanity.
"What we must do now is make sure everything is done to help in this vital phase of dealing with the floods.
"He will be invaluable as the Government embarks on the next, vital phase of its mission to restore our economy to growth and reform our public services".
Vanska has been rooting out unpublished pieces, earlier versions of well-known scores as well as scarcely performed occasional pieces, and this final volume is made up almost entirely of just such extras and additions, including the three vital phases in the evolution of one of Sibelius's most perfectly achieved works.
The SBS were used in vital phases of the invasion of Afghanistan.
Spandau were the vital extra ingredient that pushed the Blitz into its critical phase.
He is in a vital transitional phase.
"Then there's the vital recovery phase where we need to try and help people get their insurance claims and help people get back into their homes.
