The phrase "to bubble up" means to rise or emerge naturally, often without any conscious effort. It can be used in various contexts such as when referring to ideas or thoughts that come to mind spontaneously, or when discussing a situation where something rises to the surface on its own accord. The phrase is also commonly used metaphorically to describe an idea or solution that arises from brainstorming sessions or group discussions, where different opinions and suggestions "bubble up" to the surface through conversation.