Looking on the internet deeply has found these results:

speak softly is the most popular phrase on the web.

speak quietly 1190,000 results on the web	speak softly 1555,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
Could you please speak more quietly? I feel hungover. People who'd speak quietly to him in the night. I speak quietly and it suits me fine. My wife's asleep in the other room, so let's speak as quietly as we can. Could you please speak more quietly? I am feeling hungover. My heart speaks quietly and infrequently. So you must both speak very quietly or I shall shatter into a thousand little pieces. Major, I want you to keep calm, speak quietly and concentrate.	(Gandini) Being shy, discreet or speak softly (Gandini) does not work as well screen. (Gandini) Being shy, discreet or speak softly Speak softly. Speak softly, he's a famous painter. Kill those guys? "And you speak softly in my ear..."and you say things

speak quietly

1190,000 results on the web

speak softly

1555,000 results on the web

More popular!

Could you please speak more quietly? I feel hungover.
People who'd speak quietly to him in the night.
I speak quietly and it suits me fine.
My wife's asleep in the other room, so let's speak as quietly as we can.
Could you please speak more quietly? I am feeling hungover.
My heart speaks quietly and infrequently.
So you must both speak very quietly or I shall shatter into a thousand little pieces.
Major, I want you to keep calm, speak quietly and concentrate.

(Gandini) Being shy, discreet or speak softly (Gandini) does not work as well screen.
(Gandini) Being shy, discreet or speak softly
Speak softly.
Speak softly, he's a famous painter.
Kill those guys?
"And you speak softly in my ear..."and you say things