Display screen or portion thereof with transitional graphical user interface

FIG. 1 is a front view of a first image in a sequence of the display screen or portion thereof with transitional graphical user interface (“UI”), wherein heavy dash-dash lines comprise a portion of the design;

FIG. 2 is a front view of a second image in the sequence; and,

FIG. 3 is a front view of a third image in the sequence.

The subject matter in this patent includes a process or period during which an image sequentially transitions between the images shown in FIGS. 1-3 . This process or period forms no part of the claimed design.

The stippling shown in FIG. 3 comprises a decorative feature that is part of the claimed design and is meant to portray the illusion of a contrasting surface.

The broken lines rendered in thin lines including the showing of a portion of the display screen of a communications terminal surrounding the illustrated design, the illustrated chart, all text and portions of the graphical user interface are included for the purpose of illustrating the environment and form no part of the claimed design.