The ornamental design for a portion of a displayscreen with an icon, as shown and described.
FIG. 1 is a front view of the first image in the sequence for a portion of a display screen with an icon according to one embodiment of the claimed design;
FIG. 2 is a front view of the second image thereof; and,
FIG. 3 is a front view of the third image thereof.
The appearance of the portion of the display screen sequentially transitions between the images shown in FIGS. 1-3. The process or period in which one image transitions to another forms no part of the claimed design. The broken line showing a portion of a display screen and/or device for displaying the icon is for the purpose of illustrating environmental structure and forms no part of the claimed design.