AI agents call list_phone_numbers to retrieve information from Telnyx MCP Server without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
The 'list' operation is a standard Read operation that retrieves data without modifying, deleting, or executing anything. No financial transactions, destructive actions, or code execution are implied. The tool has low severity as listing phone numbers poses minimal risk even if misused by an AI agent—it only exposes metadata about phone numbers already owned or accessible to the account.
From the tool's definition Tool name is 'list_phone_numbers' which indicates a retrieval/listing operation with no side effects. The description is empty, but the semantic meaning of 'list' combined with the telephony context suggests querying existing phone numbers.
Documented attack patterns abuse exactly the kind of access list_phone_numbers gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Telnyx MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for list_phone_numbers:
{
"version": "1",
"default": "deny",
"tools": {
"list_phone_numbers": {}
}
}list_phone_numbers is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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list_phone_numbers. It is categorised as a Read tool in the Telnyx MCP Server MCP Server, which means it retrieves data without modifying state.
Register the Telnyx MCP Server MCP server in PolicyLayer and add a rule for list_phone_numbers: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Telnyx MCP Server. Nothing to install.
list_phone_numbers is a Read tool with low risk. Read-only tools are generally safe to allow by default.
Yes. Add a rate_limit block to the list_phone_numbers rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.
Set action: deny in the PolicyLayer policy for list_phone_numbers. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.
list_phone_numbers is provided by the Telnyx MCP Server MCP server (team-telnyx/telnyx-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Telnyx MCP Server, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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46 Telnyx MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.