In the poem "Song for the Deer and Myself to Return On" by Joy Harjo, the speaker seems disenchanted with the urban life in which she presently finds herself in Denver. For, she states that she is
certainly hunting something as magic as deer/in this city far from the hammock of my mother's belly.
The metaphor for the womb, the place of one's greatest security in life, and, perhaps, comfort, indicates that the speaker may feel the isolation of the city, the anonymity of living in an urban area where one can find little solace from the uncaring crowds.
From this meaningless existence, the speaker seeks refuge--something like the "hammock of [her] mother's belly--and hopes to return to the natural world that she has left that includes Louis who has taught her to call the deer who "came into this room." Louis may be the love of the speaker, and the deer are the feelings elicited by the speaker's remembrances.
I believe that this line has both a literal meaning and a figurative one.
The phrase "hammock of my mother's belly" clearly refers to the womb. As an unborn child, the speaker was cradled in this hammock.
More figuratively, I think, this phrase refers to the speaker's home -- the place that she most identifies with. In the poem, she is in this city that is far from the sort of area that really feels like home to her.
So, I believe that the phrase represents the rural area that the speaker thinks of as her true home.