Taxa abundance with plot_bar - Can the color squares in the key be reduced in size?

[atozga]

Hello,
I'm using phyloseq and plot_bar to generate taxa plots and although I'm able to reduce the size of the font in the key (using element_text) but not able to reduce the size of the color boxes which relate to the segments of the bar plot (thus making the file i export to PDF from Rstudio too big to save/visualize). Is there any way to shrink down the key NEXT to the bar plot in order to see all of the color and taxa (genera, in this case) within the chart itself? I wasn't able to find this answer anywhere else in the forum.
Thank you.
AO