Direction of movement in the phloem is bi-directional because-

Source and sink may be reversed depending on the season, or the plant’s needs. Sugar stored in roots may be mobilized to become a source of food in the early spring when the buds of trees, act as sink; they need energy for growth and development of the photosynthetic apparatus. Since the source-sink relationship is variable, the direction of movement in the phloem can be upwards or downwards, i.e., bi-directional