Will the screen size be of a phone? i want it to be the size of my laptop screen?

Yes, it can be a phone-sized display or a larger one, depending on the virtual device and skin you choose. Genymotion Desktop also supports fullscreen, so it can fill your laptop screen (Virtual Devices Settings).

You can change the primary display resolution, use fullscreen, or select a skinned window. The default skins include phone formats and tablet formats, and you can also create a custom skin if you want a specific size (Virtual Devices Settings, How to create your own skin in Genymotion Desktop?).