Page speed is a measurement of how fast the content on your page loads. Page speed measure mobile & desktop both loading time. At the moment, page speed is more of an indicator than a ranking factor. Unless mobile site is extremely slow,can still get decent rankings with average page speeds.

If page speed poor/ average in any condition then try to fix
Images size
Images scale
JS link
CS link
Minify JS/CS link

Good Condition: 0.0ms-3sec

Average Condition: 3.1sec-10sec

Poor condition: 10.1sec-60sec