Usually when a USB stick is in the laptop, you can see an eject icon in the lower right corner, but when my mobile phone is connected to the laptop, no sign appears… That's why I just pull the plug out all the time, but I think that it is not so good for the laptop… Do you know what I should do so that I can eject my cell phone or is it not necessary at all and you don't have to eject the cell phone?
USB uses different protocols for this purpose.
Nowadays the UAS protocol is used for USB sticks. The USB stick is treated like an internal hard drive and the PC mounts the file system on the USB stick. If you disconnect the USB stick from the PC during a write operation, the incomplete operation may damage the entire file system and the data can no longer be accessed easily. To prevent this from happening, there's the eject function. But this is usually unnecessary, because not even Windows just writes to USB memory in the background and you know yourself whether you are currently using the stick. This can't damage the PC at all.
The Media Transfer Protocol (MTP) is used to connect to smartphones. Since smartphones have already mounted their own file system, the PC can't mount it itself and that is therefore more of a kind of network protocol. Accordingly, it is far from having the range of functions, actually you can only copy / create / move / remove data. Because the file system is not mounted on the PC, it is also unproblematic to disconnect during a write operation. The individual file may then be damaged, but the file system remains intact.
