Fibrous materials may undergo a plastic internal reorganization, which turns out in the emergence of preferential directions. This is a peculiar behavior of many biological tissues, which drive reorientation by external stimuli at chemo-mechanical levels. In particular, it is detected that contractile cells can reorganize fibrous extracellular matrices and form dense tracts of aligned fibers (tethers), that guide the development of tubular tissue structures and may provide paths for the invasion of cancer cells [1]. Tether formation is caused by buckling instability of network fibers under cell-induced compression. These severe localizations can be brought about by mechanical forces, such as the ones due to cell contraction, without involvement of biochemical factors [2]. Due to the complete randomness of the fiber network, the virgin material can be considered homogeneous. When loaded, since some fibers buckle, a transversal anisotropy emerges; if forces are removed, the strength of those fibers can be partially recovered, but memory of the past history is retained. Starting from the results in [3], we propose to describe this process by resorting to a phase-field model, with two gross descriptors for: (i) the emergence of the anisotropy, by means of a macroscopic measure of the stiffness of fibers in the direction of the transverse anisotropy; (ii) the occurrence of the buckling, marking the material in a plastic way. We show that localization of the phase-fields may occur, which mimics the onset of tethers detected in experiments [2]. References [1] Harris, A., Stopak, D., Wild, P., Fibroblast traction as a mechanism for collagen morphogenesis. Nature 290, 249–251 (1981). [2] Grekas, G., Proestaki, M., Rosakis, P., Notbohm, J., Makridakis, C., Ravichandran, G., Cells exploit a phase transition to mechanically remodel the fibrous extracellular matrix. Journal of the Royal Society Interface, 18(175), 20200823, (2021). [3] Favata, A., Rodella, A., Vidoli, S., An internal variable model for plastic remodeling in fibrous materials, Eur. J. Mech. A Solids, Vol. 96, 104718 (2022).