Arize Phoenix is an open-source library that provides visualizing datasets and troubleshooting large language model (LLM) application development by making it easier to debug and troubleshoot LLM framework applications. It offers flexible data frameworks to connect private data to LLMs, enabling developers to gain visibility into their system with LLM orchestration frameworks like LlamaIndex, Microsoft's Semantic Kernel, and LangChain. Arize Phoenix provides a comprehensive view of the inner workings of an LLM application by breaking down the process into spans and categorizing each span with a common interface across frameworks, making troubleshooting and optimization easier and more effective. The library offers various features such as tracing, evaluating, and analyzing LLM applications to surface problems at different levels of the system, including prompt templates, token usage, runtime exceptions, retrieved documents, embeddings, LLM parameters, tool descriptions, and LLM function calls. It also supports all common spans and has a native integration into LlamaIndex and LangChain, enabling developers to get started with Arize-Phoenix in a few minutes.