Was i rude? what do you think?

At work, I am in a cubicle. My coworker in the very next cubicle speaks very loudly. I was on the phone with someone who's hard to reach (not work related but still). She started speaking very loudly to another coworker. I couldn't hear the person on the phone so I said "shh." After the call I explained to my coworker and apologized. What do you think?