What is the origin of the idiom "talk to ralph on the big white telephone" and when to use it?

The exact origin of the phrase is uncertain, but it likely developed as a funny and imaginative euphemism for the unpleasant experience of vomiting into a toilet. It is used informally and humorously to refer to the act of vomiting. It implies the imagery of someone metaphorically having a conversation with a person named Ralph while leaning over a toilet, which is often white.