How are you generating the figure?
Would the following take care of it?
ylabel('Phase')
More per clarification. There is probably an option for bodeplot to turn this off but here is a workaround that just removes it:
hFig = figure;
sys = rss(5);
h = bodeplot(sys);
labels = findall(hFig,'Type','Text');
label = labels(strncmp(get(labels,'String'),'Phase',5));
set(label,'String',regexprep(get(label,'String'),'(\(\w*))',''));
