If you mean 4 phases 7 days rounded,
The synodic period or lunation is exactly 29.5305882 days.
Depends on what you mean by "an entire phase change", the answer could be less than an hour or the answer could be 7.3 days or the answer could be 29.5 days.
"an entire phase change" is not a well-defined concept.
It takes 29.5 days to complete a full illumination phase cycle. This is known as a synodic month.
It takes a quarter of that, about 7.3 days (depending on a few specifics of the elliptical orbit) to go from "corner phase" to the next "corner phase".
What I mean by a "corner phase" is those phases that they mark on the calendar on the four select days of each synodic month. New, First quarter, Full, Third Quarter.
OF course though, the corner phases of the moon are instantaneous events. They only last for an instant.
The continuous transitional phases are Waxing Crescent, Waxing Gibbus, Waning Gibbus, and Waning Crescent.
Because the corner phases are instantaneous events, it takes infinitesimal time to get from a corner phase to the next transitional phase....or to get from a transitional phase to the next corner phase.