### Answer Based on the available documentation, I don't have specific information about a system variable for the customer's phone number that you can use in warm transfer handoff prompts. However, you can use dynamic variables in warm transfer configurations. Dynamic variables work in transfer call configurations, including warm transfer instructions. [(1) ]() [(2) ]() If you're collecting or storing the customer's phone number during the call, you could: 1. Set it as a custom dynamic variable (e.g.,

{{customer_phone}}

) and pass it when creating the call 2. Reference that variable in your warm transfer instructions For warm transfers specifically, you can configure warm transfer settings including instructions that the agent provides to the human representative. [(2) ]() I'd recommend checking if there's a system variable for the caller's number in the full dynamic variables documentation, or consider passing the phone number as a custom dynamic variable when initiating calls. If you need more specific guidance on available system variables for caller information, you might want to reach out to support or check the complete documentation. **

​ To learn more, see the sources I considered: [[1] Dynamic Variables](https://docs.retellai.com/build/dynamic-variables) [[2] Transfer call](https://docs.retellai.com/build/single-multi-prompt/transfer-call) ​

Feel free to tag @AI Evy with additional questions. I also appreciate feedback, it helps me improve.