not according to the docs, unless +a and +j are present as part of -F but without an angle and justification specification.
angle is probably not needed here, but +j and +c help with text placement that is like “top center” or “bottom left” and even +t. like:
gmt pstext -R-159.8/-154.7/18/23 -Jx2.5 -F+cBC+jTC+f11p,21+tBOTTOM -Dj0.1c -Bltrb -P -N > outfile.ps
gmt psconvert outfile.ps -Tg -A
-F+cBC+jBC is for label placement inside the frame (drawn just for illustration), +cBC+jTC places the label outside the frame so -N must be present in this case. -Dj adds offset from so the label does not overlap with the frame if there is one. -P enables portrait orientation, so no need to rotate the map afterwards.
