I am asking from a qualitative research point of view. As far as I have come to know, the model can only be formulated through grounded theory method that aims to generate theory. Could you suggest any reference that can help me justify the formulation of model in hermeneutic phenomenology.
As others have implied, any kind of observation can serve as input to your thought processes, including insights that you have gained from a phenomenological study. Grounded Theory is one way of creating theory from observations, but it is hardly the only one.
I would like to suggest that the question be re-phrased. Perhaps the question should be whether you should call your study a phenomenological study if you attempt to derive a theoretical model from it? The answer in this case is that you could, but you would rather not. You would be better advised to delve into the grounded theory literature and apply it properly, because that will be what you are actually attempting to do. Phenomenology primarily describes experiences rather than aspires to unravel causal mechanisms and theoretical underpinnings.
I would argue that as far as psychological/experiential studies are concerned, phenomenology is always the initial phase of a grounded theory (GT) research, whether acknowledged as such or not. In the case of more hermeneutic approaches, I would recommend Charmaz's constructivist approach to GT.
That said, not all models are theories. Some models are just a schematic representation of the findings, as illustrated by Braun & Clarke 2006. Thematic analysis also closely related to phenomenological analyses, though it is not as strictly bound to a philosophical background or a specific aim of delineating lived experiences.
I agree with Jacob. When you are attempting to derive a theoretical model right from the beginning, there is no point doing a phenomenological study. While a model can be described as a sense-making of the data that has been collected by the researcher, it is hard to get that out of phenomenological study which is more oriented towards describing an experience.