Checking if someone is on the phone is a common task that can be done in a few different ways. One way is to simply call the person and listen for a busy signal. If you hear a busy signal, it means that the person is already on the phone. Another way to check if someone is on the phone is to send them a text message. If the person does not respond to your text message within a few minutes, it is likely that they are on the phone.
There are a few reasons why you might want to check if someone is on the phone. One reason is to avoid interrupting them if they are in the middle of a conversation. Another reason is to find out if they are available to talk. If you are trying to reach someone who is on the phone, you can either wait until they are finished or leave a message.