The "phase of the uterine cycle from ovulation until the corpus" luteum breaks down is the

Luteal Phase

The Ovarian Cycle is composed of two phases namely the follicular phase and the luteal phase. The follicular phase( day 0-7 includes the transformation of follicles from primordial to primary to secondary to selected tertiary follicle. It ends with ovulation. Luteal Phase begins with ovulation as the corpus luteum becomes corpus albicans and degrade (day 14-28).

they float because they are less dense than the water itself

something denser than water, like a rock, will sink to the bottom