I am undertaking a piece of research work on shifting place identities and wondered what philosophical lens you prefer - Social Construction / Phenomenology and why?
Both perspectives are not mutually exclusive. In fact, constructionism was derived from phenomenology. When you consider authors like Peter Bergman, Thomas Luckmann and their highly influential book Social Construction of Reality, it has a clear phenomenological influence in it, following the works of Husserl, Heidegger, Hegel, Merleau-Ponty, Herbert Mead, Lévinas or Paul Ricoeur. The same names highly influential to the creation of postmodernism in the 70s, with phenomenology and constructionism being two of the recurring fields in which postmodern authors positioned themselves (as well as post-structuralism, which emerged during the 60s and as equally important to the postmodernist movement).
Regarding place identity, I am not versed on the subject, having only read place attachment, which I believe it is a more practical concept, mainly for how much more grounded it is.
In what manner will you engage "place"? Are we talking about a physical place? Imagined place? Or constructed placed? In any case, Erving Goffman has written about place, being a social setting in which social action and interaction took place, with meaning resulting from that. It is a recurring argument that actions give place meaning.
People can react to places they perceive as having special attributes to them, in which case the places will, themselves, become a predictor for individual action (think of religious temples, libraries or any place that has universally acknowledged rules of behaviour). But actions can also give meaning to places, like places in our memories that while public and frequented by other people hold special meaning to us for some particular reasons (where one was proposed, where we used to play as children, where we had an accident, etc). Such interactions will create meaning, construct it, if you will.
In any case, what is important to keep in mind is that places have no intrinsic meaning outside of the social realm. We, humans, attribute meaning to places based on our socialization, experiences and interactions.
I tend to say that phenomenology is preferable, as social construction presupposes the subjective element of identity while this is one of the question of your research, while phenomenology does not necessarily make this presupposition. Also, because the point of departure of phenomenology - as least as I see it - is the interrelation between a being and its environment, it provides a particular open undestanding of 'place' that connects with your research question.
for more about the method of phenomenology, see: Book Heidegger’s Concept of Philosophical Method: Innovating Phil...
Jorge André Guerreiro and Vincent Blok are actually both technically correct. Phenomenology and Social Constructivism are not mutually exclusive, and social constructivism did emerge directly as a result of phenomenology. However, Vincent Blok is also correct in clarifying that Social Constructivism, without the complement of Phenomenology, does not quite put as much emphasis on the role of "objective" forces (i.e. one's environment) that affect one's subjective and intersubjective experiences. My advice would be to approach the study by setting up a dialogue between Social Constructivism and Phenomenology, thus combining the insights that each perspective would provide on the subject.