From the poem "Phenomenal Woman" by Maya Angelou, please explain the stanzas beginning "I walk into a room" and "That's me."

In the second stanza and the two-line third stanza, the speaker explains how she is a "phenomenal woman." These stanzas are a response to the wonder in the minds of women who wish to know "where [her] secret lies."
Strangely enough, the speaker seems to be the only one who comprehends the source of her compelling attractiveness. Rather than stating one attribute such as dazzling eyes or an amazing figure, the speaker identifies her feminine power as emanating from a certain elusive quality. This quality cannot be defined, but is subtly communicated to those who perceive her in the combination of her physical traits along with her graceful movements that are generated by her energy and inner beauty:

It's the fire in my eyes,And the flash of my teeth,The swing in my waist,And the joy in my feet.

From certain words that the speaker uses, such as "fire," "flash," "swing," and "joy," the inner strength and confidence of this woman are conveyed, as these words suggest the energy and happiness that seem to charge the air when she enters a room or passes by.
Having asserted simply that she is a "Phenomenal woman" in the two-line third stanza, Angelou's speaker acknowledges that she cannot formulate her attractiveness. 
Not unlike ideas expressed in another poem of Angelou's entitled "Woman Me," the features that the speaker of "Phenomenal Woman" possesses are those that provide her an indefinable attractiveness. Her "certain something," her "phenomenon," derives from an inner source and attractiveness formed by a combination of movements and features which, though not conforming to any ideal, certainly attract men and cause women to "wonder where [her] secret lies."