Not liking the feel on lightweight stands with a heavy phone, I decided to design one that allows adding weights during the print.

Print the stand on its side with 0% infill. Feel free to scale in the Z direction for wider or narrower phones. Add a pause just before the top layers begin. During the pause add some sort of ballast. I avoided sand as I didn't want to chance spilling even a small amount. Resume the print, and enjoy.

If bridging the top isn't working well, try increasing the number of top layers.