what does the phone icon with no time mean?

[Yolo]

so i have some friends on facebook use it on their mobile device and its says 26mins which i understand they were on fb 26mins ago, then i notice some of my friends just have a phone icon with no time next to it, what does it mean when there is a phone icon without the time next to it?

[Kaiser]

If the icon is green in color ,then it means that they're using Andriod phones

[Sam]

The phone icon means they are using mobile phones but not actively. and, time means the last time they posted/did anything from their phone on facebook. i think when there is no time, it means they have gone mobile, that is they stopped using from computer and are logged in in mobile but haven't used it yet since leaving computer.